Scholarly article on N-ETHYL-N'-(4H-1,2,4-TRIAZOL-4-YL)THIOUREA 5102-45-4 from Crystal Growth and Design p. 3562

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Exploring “Triazole-Thiourea” Based Ligands for the Self-Assembly

of Photoluminescent Hg(II) Coordination Compounds

Houria Benaissa, Nayarassery N. Adarsh, Koen Robeyns, Jakub J. Zakrzewski, Szymon Chorazy,

James G. M. Hooper, Filip Sagan, Mariusz P. Mitoraj, Mariusz Wol ﬀ , Smaail Radi, and Yann Garcia*

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Supporting Information

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ABSTRACT: This study represents the ﬁrst explorative inves-

tigation on the supramolecular structural diversity in Hg(II)

coordination chemistry with triazole-thiourea ligands leading to a

variety of mononuclear, binuclear, and coordination polymers:

{[Hg(L1)₂(L1⁻)₂]} (1), {[Hg₂(L1)₂(μ₂-I)₂I₂]·DMSO} (2), {[Hg-

(L2)(μ₂-I)I]·MeOH}_∝(3), {[Hg₂(μ-L3⁻)₄]}_∝(4), {[HgCl(L4⁻)

L4]·MeOH} (5), {[Hg₂(L4)₂(μ₂-I)₂(I)₂]·2MeOH} (6),

{[Hg₂(μ₂-L5⁻)₄]}_∝(7), {[Hg₂(μ₂-Cl)₂(L6⁻)₂(L6)₂]} (8),

{[Hg₂(μ₂-Br)₂(L6⁻)₂(L6)₂]} (9), and {[Hg₂(μ₂-I)₂(L6⁻)₂(L6)₂]}

(10). A reaction mechanism was suggested for the unexpected

ligand rearrangement occurring in {[Hg₂I₃(μ₃-L5′)]}_∝(11). The

ligands were fully characterized including by X-ray crystallography

and computational means. This includes six new triazole-thiourea based ligands, namely, 1-R-3-(4H-1,2,4-triazol-4-yl)thiourea

(where R = methyl (L1), ethyl (L2), propyl (L3), isopropyl (L4), and its polymorph (L4-poly), allyl (L5), ethyl acetate (L6), and

its solvate (L6_MeOH)). Under UV light excitation, 7, 10, and 11 exhibit visible photoluminescence of wide origin, ranging from

ligand-centered (LC) ﬂuorescence combined with organic-ligand-to-metal charge transfer (LMCT) emissive states in 7 and 10, up

to halide-to-metal charge transfer (XMCT) combined with halide-to-ligand charge transfer (XLCT) emissive states in 11. The

variable emission mechanisms in the obtained coordination polymers were elucidated by experimental proofs confronted with

theoretical calculations of the electronic densities of states, proving that Hg(II) halide coordination polymers involving ﬂexible 1,2,4-

triazole-based ligands form a promising class of luminescent molecular materials.

Incorporation of hydrogen bonding functionalities (urea,

amine, amide, thiourea, etc.) within the matrix of a CP is an

excellent strategy to create a functional material which can be

useful for various applications. In order to synthesize such CPs,

two methodologies were used: (1) coordination-driven self-

assembly of a metal ion with a ligand having programmed

hydrogen bonding functionality;²⁸(2) postsynthetic modiﬁca-

tion of the CP.²⁹The resulting functional CP exhibited

unprecedented applications in sensors,³⁰gas storage,³¹

selective CO₂capture,³²catalysis,³³selective anion separa-

tion,³⁴etc., and intriguing supramolecular assembled structures

by noncovalent hydrogen bonding interactions.²⁸Moreover,

such functionalized CPs showed more competence in their

structure-dependent applications (for example, size-selective

hydrogen bond catalyst³⁵compared to the nonfunctionalized

INTRODUCTION

■

The journey of 1,2,4-triazole chemistry started with the

seminal work by Bladin in 1885.¹Even though the synthesis

of 1,2,4-triazole was established over a century ago, researchers

are still working on the design and synthesis of new 1,2,4-

triazole compounds,²due to for instance their antiviral, anti-

inﬂammatory, antimicrobial, and anticancer properties.³The

1,2,4-triazole moieties present in these biologically active

compounds justify the criteria for a potential active drug; for

example, ribavirin, ﬂuconazole, and rizatriptan are the drugs

containing 1,2,4-triazole units for treating antiviral, antifungal,

and antimigraine infections, respectively.⁴Inspired by the

coordination ability of 1,2,4-triazole ligands to form various

coordination network structures, many coordination and

material chemists including us⁵⁻¹⁰developed interesting one-

(1D), two- (2D), and three (3D)-dimensional coordination

polymer (CP) architectures.¹¹⁻¹³CPs have been recognized as

intriguing porous materials^14,15due to their fascinating

structures, and potential applications were revealed in gas

storage,^16,17separation,¹⁸heterogeneous catalysis,^19,20spin

crossover,^21,22drug delivery,²³theranostics,²⁴sensors,^25,26

optoelectronics,²⁷etc.

Received: March 29, 2021

Revised: May 1, 2021

Published: May 19, 2021

https://doi.org/10.1021/acs.cgd.1c00352

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CPs).^28,36−38Among various organic building blocks, thiourea

functionalized ligands attracted much attention, due to their

versatile coordination ability toward metal ions through the

sulfur or the nitrogen atoms or even through both of them.³⁹

The thiourea moiety exists in two mesomeric forms, namely,

thione and thiolate, and in most of the reported compounds it

showed the thiolate form (Scheme 1) due to its signiﬁcant

with Hg(II) ions have also been rarely reported.^50,51(vi)

Recently, we have found that for a given complex, the

substituents on the ligand and complex counteranions are

important components for modulating the luminescent

properties of 1,2,4-triazole complexes.⁵¹We therefore antici-

pate that the current triazole-thiourea ligands are potential

candidates for the detection of Hg by the formation of

luminescent complexes, which is environmentally relevant as

mercury and its derivatives are known to be highly toxic

pollutants.⁵²⁻⁵⁴

Scheme 1. Mesomeric Forms (Thione and Thiolate) of the

a

Ligands L1−L6

In the present account, we introduce the crystal structures of

a series of new 1,2,4-triazole ligands functionalized with

thiourea L1 to L6 (Scheme 2) and their corresponding Hg(II)

a

Scheme 2. Chemical Structures of the Triazole-Thiourea

R = Me, Et, prop, iso-prop, allyl, and COOCH₂CH₃for L1, L2, L3,

L4, L5, and L6 respectively.

Based Ligands L1−L6

donor strength to the metal ion via a coordination bond.^40,41

Moreover, a Cambridge structure database (CSD)⁴²search on

compounds of thiourea based ligands^43,44showed the presence

of characteristic intermolecular N−H···S hydrogen bonding,

with dominant N−H···OC and N−H···SC hydrogen

bond interactions.^45,46

Our research on the crystal engineering and functional

properties of 1,2,4-triazole ligands,⁴⁷and their CPs,⁵led us

recently to investigate the structural diversities of two 1,2,4-

triazole ligands, namely, 4H-1,2,4-triazol-4-yl-acetate and 4-

(4H-1,2,4-triazol-4-yl)-^L-propionic acid as a function of the

hydrogen bonding functionality attached to the 1,2,4-triazole

ligand such as the ester and carboxylic acid, respectively.⁴⁷In

these studies, the ester and carboxylic acid moiety function-

alized with 1,2,4-triazole played a signiﬁcant role for the self-

assembly process, which led to the formation of homochiral

helical chains and 2D hydrogen bonded networks, respectively.

We have also recently studied the eﬀects of conformational

ﬂexibility and hydrogen bonding of the 1,2,4-triazole ligands,

on the ﬁnal outcome of CPs.⁶⁻⁹In such studies, the 1,2,4-

triazole ligand backbone contains hydrogen bonding carboxylic

acid and ester functionalities, which help to interact with

solvent molecules and counteranions, and lead to hydrogen

bonding assisted self-assembled supramolecular structures.

Such compounds showed unusual robustness and thermal

stability, and allowed for gas adsorption⁷⁻⁹and storage of

metallic mercury.⁶

coordination compounds. We shall explore the eﬀect of

hydrogen bonding and metal coordination capability of

thiourea functionality of the ligands on the supramolecular

structures of the new coordination compounds. We also aim to

correlate the luminescent properties of our compounds to their

crystal structures. For this purpose, density function theory

(DFT) calculations have been performed to assess the nature

of the observed emission.

RESULTS

■

Synthesis and General Characterization. The ligands

were prepared according to the procedure described by

Bielenica et al.⁵⁵involving the reaction of 4-amino-1,2,4-

triazole and SCN-R, R being methyl (L1), ethyl (L2), propyl

(L3), isopropyl (L4), allyl (L5), and ethyl formate (L6)

(Scheme 3). The resulting asymmetric molecules contain a

Inspired by these functional CPs and their intriguing

properties, we decided to functionalize the 1,2,4-triazole with

a thiourea moiety (Scheme 1) and study their self-assembly

properties as well as their coordination abilities toward the

mercury ion due to its enormous negative impact on our

environment. This study was also motivated by the following

reasons: (i) thiourea molecules having nitrogen and sulfur

donors atoms have shown their ability to provide variable

bonding modes and structural diversity in coordination

chemistry.^48,49(ii) Thiourea is expected to participate to

hydrogen bonding interactions with multiple partners (i.e.,

counteranions, 1,2,4-triazole groups, lattice included or metal

bound solvent molecules, and even other thiourea functions).

(iii) Nitrogen heteroatoms from the 1,2,4-triazole building

block are suitable for coordination with metal ions and can

lead to CP formation. (iv) CPs involving triazole-thiourea

based ligands have not been reported, and there are no Hg(II)

complexes with such ligands reported so far, thus increasing

interest of the present report. (v) Metal-triazole complexes

Scheme 3. Schematic Representation of the Synthesis of the

Ligands

thiourea backbone with 1,2,4-triazole on the other side. This

asymmetric nature allows the yield to energetically favorable

conformations in their free ligand form and in their

coordinated form in Hg coordination compounds.

Reaction of such ligands with mercury salts provided 10

coordination compounds which were all crystallized, using

either slow evaporation or slow diﬀusion methods (using a

branched Γ tube). The compounds were characterized by FT-

IR, UV−visible, elemental analysis, and powder X-ray

diﬀraction (PXRD). The compounds were found to be air

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and light sensitive over time, as well as hygroscopic. The crystal

structures of all compounds were determined by single crystal

X-ray diﬀraction (SXRD) providing the following formulas:

{[Hg(L1)₂(L1⁻)₂]} (1), {[(Hg)₂(L1)₂(μ₂-I)₂(I)₂]·DMSO}

(2), {[Hg(L2)(μ₂-I)I]·MeOH}_∝(3), {[Hg₂(μ-L3⁻)₄]}_∝(4),

{[HgCl(L4⁻)L4]·MeOH} (5), {[Hg₂(L4)₂(μ₂-I)₂(I)₂]·

2MeOH} (6), {[Hg₂(μ₂-L5⁻)₄]}_∝(7), {[Hg₂(μ₂-Cl)₂-

(L6⁻)₂(L6)₂]} (8), {[Hg₂(μ₂-Br)₂(L6⁻)₂(L6)₂]} (9),

{[Hg₂(μ₂-I)₂(L6⁻)₂(L6)₂]} (10), and {[Hg₂I₃(μ₃-L5′)]}_∝

(11).

Scheme 4. Plausible Conformations of the Ligands L1−L6

1-Methyl-3-(4H-1,2,4-triazol-4-yl)thiourea (L1). The tria-

zole-thiourea molecule L1 crystallizes in the centrosymmetric

monoclinic P2₁/n space group (Table S1). The asymmetric

unit contains one molecule of L1 and one molecule of lattice

included water. From the crystal structure, it is found that the

ligand is nonplanar, in which the triazole ring and the thiourea-

methyl functionalities are almost perpendicular to each other

[the torsion angle between the triazole and thiourea is

83.35(13)°], and shows anti-syn conformation (Scheme 4).

The lattice water molecule stabilizes the structure by hydrogen

bond interactions with three neighboring molecules of L1,

acting as an acceptor for the N−H group of thiourea adjacent

to the 1,2,4-triazole ring, while hydrogen bonding to both

nitrogens of the N−N bond of L1, one on each side. A

FT-IR Spectroscopy. The ligands and coordination

compounds were investigated by solid-state Fourier transform

infrared spectroscopy (FT-IR) over the range 4000 to 400

cm⁻¹by using KBr pellets. The comparison plots are provided

in the Supporting Information (SI). The FT-IR stretching and

bending frequencies of ligands and the corresponding

coordination compounds showed similarity in the correspond-

ing characteristic peaks. In the FT-IR spectra of 1 and 2, the

band at 3170 and 3134 cm⁻¹, respectively, was found to shift

(3109 cm⁻¹) from the corresponding ligand L1. This band is

attributed to the characteristic thiourea N−H stretching.⁵⁶The

characteristic IR absorption peaks belonging to the 1,2,4-

triazole ring such as C−H aromatic vibrations (3088 and 2936

cm⁻¹for L1, 3089 and 2970 cm⁻¹for 1, 3109 and 2938 cm⁻¹

for 2), CC stretching (1520 and 1440 cm⁻¹for L1, 1512

and 1498 cm⁻¹for 1, 1520 and 1444 cm⁻¹for 2), and NN

stretching (1572, 1576, and 1572 cm⁻¹for L1, 1 and 2,

respectively) were also observed in the FT-IR spectrum of the

free ligand L1 and the corresponding complexes 1 and 2. In

addition, the band appearing at 1237 cm⁻¹due to thiourea

CS stretching in the free ligand L1 was downward shifted to

1210 and 1183 cm⁻¹in the IR spectra of complexes 1 and 2,

respectively, indicating the coordination through the thiourea

sulfur atom.⁵⁷The coordination of Hg(II) with the S atom of

the thiourea moiety of the ligand was conﬁrmed by the IR

band at 571 and 567 cm⁻¹for 1 and 2, respectively, attributed

to the Hg−S stretching frequency. Similarly, the FT-IR

spectrum of compounds 3, 4, 5, 6, 7, 8, 9, 10, and 11, and

their corresponding ligands showed N−H stretching of

thiourea, C−H, CC, and NN aromatic stretching

vibrations (all the three belong to 1,2,4-thiourea functionality),

thiourea CS, and metal−ligand Hg−S stretching vibrations

(Table S5).⁵⁸⁻⁶¹

4

macrocyclic ring structure with graph set notation R₄(14) is

constructed by a N atom of the triazole, the N−H of thiourea,

and the water molecule [O−H···N = 2.926(12) Å, ∠O−H−N

= 148.06°; N−H···O = 2.741(14) Å, ∠N−H−O = 153.75°].

Such 0D hydrogen bonded macrocycles interact with each

other through hydrogen bonding, resulting in the formation of

a 2D hydrogen bonded supramolecular network structure.

TOPOS analysis^62,63suggests that it is a 2D hydrogen bonded

network with Point symbol {4.8^2.10^3}{4.8^2}. The 2D

hydrogen bonded network was further packed on top of each

other, with the support of N−H···S hydrogen bonding

involving thiourea functionalities; N−H···S is dominated by a

homosynthon formation between two adjacent thiourea across

2

an inversion center, forming a R₂(8) ring [N−H···S =

3.3752(19) Å, ∠N−H−S = 164.46°] (Figure 1).

1-Ethyl-3-(4H-1,2,4-triazol-4-yl)thiourea (L2). The ethyl-

thiourea derivative of 1,2,4-triazole L2 also crystallizes in the

centrosymmetric monoclinic space group P2₁/n (Table S1),

with a single molecule in the asymmetric unit. The ligand

exhibits a nonplanar conformation in which the 1,2,4-triazole

ring and the thiourea-ethyl functional groups were found

almost orthogonal to each other (torsion angle of 84.29°).

Ligand L2 showed syn-anti conformation (Scheme 4), as

opposed to L1. As a result, the observed homosynthon is

UV−Visible Spectroscopy. UV−visible absorption spec-

tra of the molecules L1−L6 and coordination compounds were

recorded in the solid state over the range λ = 200−800 nm

(spectra are shown in Supporting Information). The electronic

spectra of ligands showed absorption bands exclusively in the

UV region, corresponding to intraligand transitions such as

π−π* and n−π*. Similar bands were also observed in the

spectra of the corresponding coordination compounds,

although they were red-shifted.

2

formed with the NH adjacent to the triazole moiety (R₂(8)

ring), contrary to L1 where the other NH group was acting as

a donor [N−H···S = 3.248(8) Å, ∠N−H−S = 165.87°]. The

other NH moiety is equally involved in a ring structure

2

R₂(14), linking two molecules through an interaction with a

Single Crystal X-ray Diﬀraction. Details of the data

collection and reﬁnement are given in Table S1. Topological

analysis of the nets was performed using the TOPOS program

package.^62,63

Crystal Structures of Triazole-Thiourea Molecules.

The ligands L1−L6 are expected to show four possible

conformations “syn-syn”, “anti-anti”, “syn-anti”, and “anti-syn”,

in which the hydrogen atoms of thiourea function near the

1,2,4-triazole ring and alkyl/allyl/ethyl formate are on the same

side (or face), opposite side, same and opposite side, opposite

and same side, of thiourea, respectively (Scheme 4).

triazole nitrogen [N−H···N = 2.956(14) Å, ∠N−H−N =

152.74°]. The combination of both interactions leads to the

formation of 1D zigzag hydrogen bonded chains (Figure 2).

Interestingly, the adjacent hydrogen bonded chains are packed

in a parallel fashion sustained by interactions of both triazole

C−H hydrogens with a triazole N and the thiourea S atom on

either side of the triazole. [C−H···N = 3.358(6) Å, ∠C−H−N

= 148°; C−H···S = 3.79(10) Å, ∠C−H−S = 153°], forming a

2D layer expanding in the ab plane. In the c directions, these

planes are oﬀset in an almost orthogonal fashion, exposing the

hydrophobic ethyl groups to one another.

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L2, also forming 2D layers, consecutive 2D layers do not show

an orthogonal oﬀset but rather a parallel displacement between

stacked layers in the c direction.

1-Isopropyl-3-(4H-1,2,4-triazol-4-yl)thiourea (L4). L4, iso-

propyl analogue and isomer to L3, crystallizes in the

̅

centrosymmetric triclinic P1 space group (Table S1), with

one molecule in the asymmetric unit. L4 exhibits a nonplanar

syn-anti conformation (Scheme 4) as L2 and L3, in which the

triazole and thiourea moiety are orthogonal to each other

having a torsion angle of 86.16°. As observed in the crystal

structure of L2 and L3, similar hydrogen bond patterns are

2

present: the R₂(8) ring involving N−H···S [N−H···S =

2

3.225(2) Å, ∠N−H−S = 163°] as well as the R₂(14) ring

[N−H···N = 2.999(13) Å, ∠N−H−N = 155.04°]. These

hydrogen bonds lead to the formation of a zigzag chain, and

expansion of the C−H interactions of the triazole also leads to

2D layers, which in L3 show a parallel displacement between

consecutive layers (see Figure S2). A polymorph of L4 was

Figure 1. Crystal structure illustration of L1. (a) asymmetric unit of

L1; (b) 14-membered hydrogen bonded macrocycle with graph set

̅

also obtained (L4-poly), also crystallizing in P1, with a slightly

larger unit cell volume. On the molecular level, both structures

4

2

R₄(14); (c) R₂(8) ring formed by the self-complementary thiourea

hydrogen bonding; (d) 2D hydrogen bonded sheet formed from the

self-assembly of hydrogen bonded macrocycles (one of such

macrocycles is shown in space ﬁll model); (e) TOPOS view of 2D

hydrogen bonded sheet; (f) parallel packing of 2D hydrogen bonded

sheets through thiourea hydrogen bonding, displaying two distinct

synthons.

2

are quite similar, showing similar R₂(8) rings between the

thiourea groups. Because of subtle conformational diﬀerences,

2

the R₂(14) ring is however formed with the other triazole

nitrogen, thus disrupting the 2D layers formed by interactions

with the triazole C−H groups. In L4-poly, the isopropyl and

the adjacent N−H are found disordered over three sites, which

2

might indicate that the R₂(14) ring shows less favorable

hydrogen bond interactions (Figure S3).

1-Allyl-3-(4H-1,2,4-triazol-4-yl)thiourea (L5). The allyl−

thiourea derivative of 1,2,4-triazole molecule L5 crystallizes in

the centrosymmetric monoclinic space group P2₁/n, with one

molecule of L5 in a general position (Table S1). The triazole

ring and the thiourea functionalities showed nonplanar anti-syn

(see L1) conformation (Scheme 4), having a torsion angle

2

between them of around 83.89°. L5 shows an identical R₂(8)

ring homosynthon as L1 [N−H···S = 2.746(10) Å, ∠N−H−S

= 141.73°], and the interaction with the water molecule of the

NH adjacent to the triazole in L1 is substituted by a hydrogen

bond with a neighboring triazole. This interaction restricts the

propagation of hydrogen bond interactions to wavy 2D layers

having a hexagonal grid topology. The 2D sheets are further

packed exactly on top of each other along crystallographic axis

“a”, sustained by various supramolecular interactions involving

the triazole, C−H···S [C−H···S = 3.664(8) Å, ∠C−H−S =

160°] and C−H···N [C−H···N = 3.280(2) Å, ∠C−H−N =

155°] (Figure 3).

Figure 2. Crystal structure illustration of L2. (a) Asymmetric unit of

L2; (b) crystal packing of L2 molecules within the unit cell; (c) 1D

zigzag hydrogen bonded chain, around the crystallographic axis “a”

(hydrogen atoms were omitted for clarity); (d, e) orthogonal packing

of 1D zigzag chains (parallel packed 1D chains are shown in red).

Ethyl 2-(4H-1,2,4-Triazol-4-yl)acetate Thiourea (L6). L6

crystallizes in the orthorhombic space group Pbca (Table S1),

with a single molecule in the asymmetric unit. L6 exhibits

nonplanar anti-syn conformation (see L1 and L5) (Scheme 4),

in which the triazole and thiourea moiety are orthogonal to

each other having a torsion angle of 85.68°. In the crystal

1-Propyl-3-(4H-1,2,4-triazol-4-yl)thiourea (L3). L3 equally

crystallizes in the centrosymmetric monoclinic space group

P2₁/n (Table S1). The asymmetric unit comprises one

molecule of L3. The thiourea derivative ligand L3 adopts a

nonplanar geometry with syn-anti conformation (Scheme 4) as

in L2; the triazole ring and thiourea moiety are almost

orthogonal to each other with a torsion angle of 84.75°. The

2

structure, L6 molecules lack the R₂(8) ring homosynthon

involving the S atom, and L6 is rather characterized by a

bifurcated hydrogen bond engaged in an intra- and

intermolecular interaction with the carbonyl oxygen of the

ester group [N−H···O = 2.642(2) Å, ∠N−H−O = 133°

(intra); N−H···O = 3.018(2) Å, ∠N−H−O = 132°]. L6

undergoes further classical intermolecular hydrogen bonding

through thiourea···triazole [N−H···N = 2.854 (2) Å, ∠N−H−

N = 165°], and such hydrogen bonding resulted in a

hexagonal-shaped macrocycle, which is the primary synthon.

Extension of such hydrogen bonding resulted in a 2D

2

syn-anti conformation allows an identical R₂(8) ring

homosynthon as in L2 [N−H···S = 3.256(2) Å, ∠N−H−S =

2

164°]. The R₂(14) ring is also observed, similar to L2 [N−

H···N = 2.939(3) Å, ∠N−H−N = 152°]. Such hydrogen

bonding leads to the formation of 1D zigzag hydrogen bonded

chains. While L3 exhibits similar hydrogen bonding patterns as

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Crystal Structures of Coordination Compounds.

{[Hg(L1)₂(L1⁻)₂]} (1). Single crystals of complex 1 were

grown from MeOH by reacting Hg(NCS)₂and L1 in a 1/3

ratio and crystallized in the tetragonal space group I4 (Table

S1). The central Hg(II) atom is located on the crystallographic

4-fold axis, with four symmetry equivalent ligands coordinated

through the S atoms, without any thiocyanato anions. Thus,

the crystal structure of 1 is described as a mononuclear Hg(II)

complex, tetra-coordinated by L1, having the formula {[Hg-

(L1)₂(L1⁻)₂]}. Charge neutrality was indeed achieved by

deprotonation of two ligands; as the four ligands are

crystallographically identical, the charge is spread out over all

four ligands, and the N−H hydrogen next to the triazole is

reﬁned as half occupied. The ligand was found to be

disordered over two positions [site occupancy factor =

0.69462 and 0.30538]. The major part shows the “syn-anti”

conformation as in the free ligand, while the minor part is

found in the “anti-anti” conformation (Scheme 4). In the

crystal structure of 1, ligand L1 displays an orthogonal

arrangement between triazole−thiourea (dihedral angle of

89.76°) in the major part, and the minor part shows a more

planar structure with a dihedral angle of 21.02°. The

coordination around Hg(II) for the major and minor part is

best described as a near perfect square pyramid (τ₄= 0.95 and

1.08, respectively). We recall that τ = 0 for square pyramidal

and τ = 1 for trigonal-bipyramidal arrangement, with τ is

deﬁned by the ratio (β − α)/60° where β > α are the two

greatest angles of the coordination center (Figure 5).⁶⁴

Figure 3. Crystal structure illustration of L5. (a) Asymmetric unit;

(b) N−H···S with graph set of R₂(8); (c) N−H···N hydrogen

bonding; (d) 2D hydrogen bonded sheet formed as a result of N−H···

N and N−H···S hydrogen bonding; (e) TOPOS view of overall

packing of 2D hydrogen bonded networks displayed in various

crystallographic axes.

2

hydrogen bonded hexagonal-shaped network. The 2D sheets

are further packed on top of each other in an oﬀset fashion

(along crystallographic axis “b”, sustained by C−H···N [C−

H···N = 3.141(4) Å, ∠C−H−N = 121°], involving triazole

(C−H)···triazole (N) (Figure 4). A solvate of L6, L6_MeOH

was also found and shows the same bifurcated hydrogen. The

MeOH oxygen takes the place of a triazole in the thiourea···

triazole hydrogen bond found in L6, disrupting the 2D sheets

and converting them in a zigzag layer (Figure S4).

{[Hg₂(L1)₂(μ₂-I)₂I₂]·DMSO} (2). The Hg(II) binuclear

complex 2, which was prepared by reacting HgI₂and L1 in

MeOH, crystallized in the centrosymmetric triclinic P1 space

̅

group (Table S1). The unit cell contains one binuclear

complex, found on an inversion center and two non-

coordinated molecules of dimethyl sulfoxide (DMSO). Two

iodine anions bridge the two Hg(II) centers, and the trigonal

pyramidal (τ₄= 0.78) coordination is further completed by a

third iodine anion, and one molecule L1, coordinated through

Table S4 lists the hydrogen bond parameters for the

reported ligands and complexes.

Figure 4. Crystal structure illustration of L6. (a) Asymmetric unit; (b) packing of L6 molecules in unit cell; (c) hexagonal-shaped hydrogen

bonded macrocycle, sustained by N−H···O and N−H···N hydrogen bonding; (d) 2D hydrogen bonded network, formed by the self-assembly of

hydrogen bonded macrocycles (along crystallographic axis “a”); (e) TOPOS view of 2D hydrogen bonded network, displaying the hexagon-shaped

topology; (f, g) oﬀset packing of 2D sheets along various crystallographic axes.

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{[Hg(L2)(μ₂-I)I]·MeOH}_∝(3). The coordination polymer 3,

which was prepared by reacting HgI₂and L2 in a 1/1 ratio in a

MeOH/THF mixture, crystallized in the monoclinic space

group P2₁/c (Table S1). The asymmetric unit comprises one

Hg(II), one molecule of L2, two iodide anions (both L2 and

iodide are coordinated to the metal center), and one molecule

of lattice included methanol (MeOH) entrapped in the crystal

lattice. The Hg(II) metal center shows a distorted trigonal

pyramidal geometry [τ₄= 0.77] in which three positions are

coordinated by iodide anions, and the fourth coordination site

is occupied by a S atom of the thiourea group of ligand L2.

Two positions of the iodine atoms around every Hg(II) center

are symmetry related, resulting in extended coordination

polymerization, which leads to the formation of a 1D

coordination polymer. This type of 1D coordination chain of

{-Hg−I−Hg−I−Hg-}_∝is commonly found in Hg(II) CPs.^65,66

The ligand showed nearly identical conformation as in the free

ligand L2 (syn-anti conformation, RMSD 0.37 Å between the

2

free and complexed L2 ligand) and a similar R₂(8) ring

homosynthon as in the free L2 ligand interactions [N−H···N =

2.977(6) Å, ∠N−H−N = 151.29°], resulting in the formation

of 2D hydrogen bonded corrugated sheet-like architecture.

The π···π stacking interactions involving the 1,2,4-triazole rings

further strengthen this 2D corrugated sheet [centroid···

centroid = 3.448 Å]. In the crystal structure, the lattice

included MeOH molecule is found to be hydrogen bonded

with the thiourea nitrogen atom of the 2D sheet, and 1,2,4-

triazole nitrogen atom of the adjacent 2D sheet [N−H···O =

2.729(12) Å, ∠N−H−O = 143.95°; O−H···N = 2.823 (8) Å,

∠N−H−O = 179.68°]; this hydrogen bonding leads to the

formation of a 3D hydrogen bonded network structure (Figure

7).

Figure 5. Crystal structure illustration of 1. (a) Asymmetric unit; (b)

stick representation of the ligand as observed in 1; major part in cyan

(top), minor part in magenta (bottom) ; (c) disorder of the ligand

molecule over two positions (shown in red and blue; Hg(II) is shown

in magenta); (d) mononuclear Hg(II) complex with a 1:4 metal to

ligand stoichiometric ratio with coordinated sulfur atoms in red. (e) 1

showing the observed disorder.

the thiourea sulfur atom. Ligand L1 displays a nonplanar

geometry with a “syn-anti” conformation (Scheme 4), contrary

to the anti-syn conformation of the free ligand and shows a

dihedral angle of 88.19°, between thiourea and the triazole

ring. The Hg(II) binuclear complex exhibits N−H···N

hydrogen bonding [N−H···N = 2.861(2) Å, ∠N−H−N =

152.92°] between the thiourea and triazole, resulting in a 1D

hydrogen bonded chain, leading to the formation of a 14-

{[Hg₂(μ-L3⁻)₄]}_∝(4). Single crystals of the coordination

polymer 4, which was prepared by reacting HgCl₂and L3 in

MeOH in a 1/1 ratio, belong to the monoclinic space group Pn

(Table S1). The asymmetric unit contains two crystallo-

graphically independent Hg(II) ions and four crystallo-

graphically independent ligand molecules. The Hg(II) centers

coordinate to four L3 ligands through N and S atoms of 1,2,4-

triazole and thiourea moieties, respectively, bridging the metal

centers in all directions. The propyl group of two ligand

molecules is disordered over two positions. The metal center

displays a slightly distorted trigonal pyramidal geometry [τ₄=

2

membered hydrogen bonded macrocycle of graph set R₂(14).

Additionally, π···π stacking interactions are present in this

macrocycle between 1,2,4-triazole moieties [distance between

the triazole ring centroids = 3.506 Å]. The N−H adjacent to

the triazole shows a hydrogen bond to the DMSO oxygen

(Figure 6).

Figure 6. Crystal structure illustration of 2. (a) Binuclear Hg(II) complex displaying the bridging of iodide anions between the Hg(II) ions; (b)

hydrogen bonding and π···π stacking interactions in 2; (c) 1D hydrogen bonded chain sustained by N−H···N hydrogen bonding, displaying the

occlusion of DMSO (space ﬁll model) within the interstitial space.

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Figure 7. Crystal structure illustration of 3. (a) Asymmetric unit containing the monomer unit of CP 3 and lattice included MeOH; (b) 1D CP

displaying the {-Hg−I−Hg−I−Hg-}_∝units (Hg and I atoms are shown in magenta and cyan color, respectively), and apically coordinated ligand

L2; (c) TOPOS view of the backbone of the CP (Hg, I, and N atom of triazole are shown in red, green, and blue); (d) extension of 1D CP to a 2D

hydrogen bonded corrugated sheet structure sustained by N−H···N and π···π stacking interactions; (e) TOPOS view of the 2D sheet; (f) a close

look of N−H···N hydrogen bonding; (g) parallel packing of 2D corrugated sheets (adjacent sheets are shown in purple and orange); (h) overall

packing of 2D sheets, displaying the inclusion of MeOH (shown as a space ﬁll model) within the interstitial space of the sheets (adjacent sheets are

shown in purple, blue, orange, and green).

0.77 and 0.73]. While HgCl₂was used as the starting salt, the

crystal structure does not contain any chloride anions. Actually,

a closer look at the crystal structure revealed that the positive

charges of Hg(II) are balanced by the deprotonated form of

ligand L3 (the deprotonation takes place from the thiourea

N−H, adjacent to the triazole ring). The N−N bond length

involving the triazole N atom and thiourea N atom showed a

slight increase from 1.386(2) Å in the free ligand to a range of

1.394(8)−1.416(11) Å in the CP, further conﬁrming the

deprotonation. The ligand L3 exhibits anti-syn conformation,

contrary to the free ligand that showed the syn-anti

conformation, in which the dihedral angle between thiourea

and triazole ring are in the range of 64.03−78.41°. The

extended coordination of L3 with Hg(II) resulted in the

formation of a 2D square grid coordination polymer with

corrugated sheet-like architecture. The thiourea N−H exhibits

intramolecular hydrogen bonding with the N atom of 1,2,4-

triazole (see Supporting Information), which further stabilizes

the 2D corrugated sheet. Such sheets are packed on top of each

other along the crystallographic axis “a” in a slight oﬀset

fashion, supported by various supramolecular interactions

(Figure 8).

̅

space group P1 (Table S1). The asymmetric unit contains two

crystallographically independent Hg atoms, each of which is

coordinated to two molecules of L4 (through the S atom of the

thiourea) and to one chloride anion [Hg−Cl = 2.541(11)−

2.548(8) Å; Hg−S = 2.395(5)−2.409(5)] in a distorted

trigonal planar geometry, forming a mononuclear complex. For

one of the discrete complexes 5, both L4 isopropyl groups

were found disordered over two positions. The four MeOH

solvent molecules found in the unit cell are also disordered

over two sites. Bond valence analysis indicates that both Hg

centers are in the +2 state, for which the charges are counter

balanced by one Cl⁻anion and a deprotonated L4⁻ligand. In

all L4 ligands, the N atom adjacent to the triazole is

deprotonated, and all show the anti-syn conformation, contrary

to the free ligand that was found in the syn-anti conformation,

but in one of the two L4 ligands on every Hg center the 1,2,4-

triazole is protonated, forming a hydrogen bond with the

deprotonated triazole of a symmetry related complex, in a

2

R₂(28) ring [N−H···N = 2.71(3) Å, ∠N−H−N = 161° or

N−H···N = 2.70(3) Å, ∠N−H−N = 157°]. The complexes are

further stabilized by intramolecular hydrogen bonds between

the thiourea N−H and the Cl atom. The formation of the

hydrogen bonded macrocycles results in two solvent channels

running along the a-axis. In both channels, disordered MeOH

molecules are located. The disordered nature of the MeOH

{[HgCl(L4⁻)L4]·MeOH} (5). Single crystals of complex 5

formed by the reaction of HgCl₂and L4 in a 1/1 ratio in a

MeOH/THF mixture belong to the centrosymmetric triclinic

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∠N−H−N = 144.39°], expanding into a 1D chain, which are

held together by the lattice MeOH solvent molecules.

Figure 10. Stick representation of 6 showing identical hydrogen

patterns as in the free ligand L4 (superposed in magenta).

{[Hg₂(μ₂-L5⁻)₄]}_∝(7). Single crystals of the coordination

polymer 7, which were prepared by reacting HgCl₂and L5 in a

1/1 ratio in a mixture of MeOH/THF, crystallized in the

monoclinic space group Pn and displayed similar cell

dimensions and packing as observed in 4 (Table S1). Ligands

L5 and L3 show the same conformation in 7 and 4,

respectively, and the small conformational diﬀerences between

the isostructural complexes are located between the allyl or

propyl moieties. Figure 11 shows the superposition of 7 and 4,

with near perfect overlap.

Figure 8. Crystal structure illustration of 4. (a) 2D corrugated square

grid CP, displaying the distorted trigonal pyramidal geometry of

Hg(II) and the coordination modes of ligand L3; (b) TOPOS view of

2D corrugated square grid CP; oﬀset packing of the square grid CPs

along crystallographic axis “a” (c) and “b” (d) (adjacent CPs are

shown in blue and red).

molecules and the absence of any interactions with the

complexes suggest that the MeOH molecules might migrate

through the channels (Figure 9).

{[Hg₂(L4)₂(μ₂-I)₂I₂]·2MeOH} (6). 6, which was prepared by

reacting HgI₂and L4 in a 1/1 ratio in a MeOH/THF mixture,

crystallizes in a centrosymmetric triclinic space group P1

̅

(Table S1), revealing a binuclear complex formed by the self-

assembly of Hg(II) salt of iodide and L4. The unit cell

comprises a single complex 6, with two μ₂bridging iodine

atoms and two lattice MeOH molecules. The Hg(II) metal

center showed distorted tetrahedral geometry [τ₄= 0.79], in

which three coordination sites are occupied by iodide anions,

and the remaining fourth was coordinated with S atom of the

ligand L4. The ligand L4 showed syn-anti conformation as in

the free ligand L4, the dihedral angles involving the thiourea

and triazole ring being 78.73°. As in the free ligand L4, the N

atoms of the 1,2,4-triazole group of L4 form a homodimer

Figure 11. Superposition of 7 onto 4 (magenta), showing near perfect

overlap, also between the ligands L5 (allyl) and L3 (propyl).

[Hg₂(μ₂-Cl)₂(L6⁻)₂(L6)₂]} (8), {[Hg₂(μ₂-Br)₂(L6⁻)₂(L6)₂]} (9),

and {[Hg₂(μ₂-I)₂(L6⁻)₂(L6)₂]} (10). The single crystals of 8, 9,

and 10 were obtained by the reaction of L6 with HgCl₂,

HgBr₂, and HgI₂, respectively, in a 1:1 metal−ligand

stoichiometric ratio. Structure determination revealed that

the structures of 8, 9, and 10 are isomorphous and crystallized

2

synthon (R₂(14) ring) (Figure 10) [N−H···N = 3.057(6) Å,

2

Figure 9. (a) R₂(28) ring macrocycle formed by hydrogen bond interactions, showing intramolecular hydrogen bonds with the chlorine atom

(green) in 5. (b) Solvent channels shown where the disordered MeOH molecules are located.

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Figure 12. Crystal structure illustration of 8. (a) Hg(II) binuclear complex 8; (b) 1D hydrogen bonded chain; (c) 2D hydrogen bonded sheet; (d)

TOPOS view of 3D hydrogen bonded network structure. Disorder on the alkyl chain was omitted for clarity.

in centrosymmetric triclinic space group P1

̅

(Table S1). The

and the triazole N atom in the apical position; the C−Hg−I

bond angle is near linear, 177.3(9)°. The Hg−I distance

conﬁrmed the oxidation states of Hg with 2.606−2.657 Å. The

positive charges of the Hg are balanced by the coordinated

iodide as well as the δ⁺charge on the allylic carbon atoms

coordinated to Hg(II) ions. While one Hg(II) metal center

shows distorted trigonal pyramidal geometry [∠N−Hg−I =

97.2(3)−101.5(3)°; ∠I−Hg−I = 143.45(6)°; ∠N−Hg−S =

89.0(3)°; ∠I−Hg−S = 105.55(10)−105.93(10)°], the Hg(II)

ion coordinated to an allylic carbon atom displays a distorted

linear geometry [∠C−Hg−I = 177.3(9)−177.3(9)°]. On the

other hand, the trigonal pyramidal coordination geometry of

Hg(II) is surrounded by a N atom of the triazole (apical

position) of L5′, two iodide and S atoms of thiourea of ligand

L5′ (equatorial positions). The iodide anions do not

participate in any bridging coordination. The extended

coordination of N and S atoms of the triazole and thiourea

functionalities of L5′ with both Hg atoms leads to the

formation of a 1D CP. In L5′, the twist angle between the ﬁve-

membered rings is about 73° and the bend character leads to

the formation of a 1D zigzag CP along the two-fold screw axis

(Figure 13).

unit cell contains a single binuclear complex with two (μ₂)

bridging halide anions and two S-coordinated L6 ligands on

either Hg atom (Figure 12). One of the L6 ligands is in the

anti-anti, the other in the anti-syn conformation, in which the

triazole ring and thiourea moieties are almost perpendicular

with dihedral angles of 78.57° & 88.20°, 80.63° & 86.21°, and

82.42° & 87.50°, for 8, 9, and 10 respectively. The ligand in

the anti-anti conformation is deprotonated as L6⁻to maintain

the charge balance of the Hg(II) metal center. The Hg

coordination is described as a distorted to near perfect trigonal

pyramid [τ₄= 0.79 (8), τ₄= 0.82 (9), τ₄= 0.84 (10)]. The

binuclear complex self-assembled into a 3D hydrogen bonded

network structure, and the main hydrogen bonds involve a

2

dimeric R₂(8) ring between the thiourea moieties of

neighboring deprotonated L6 ligands [N−H···N =

2.995(4)Å, ∠N−H−N = 150.34°]. The 3D network is further

completed by 1D hydrogen bonded chains in the other

directions with the support of N−H···N interactions [N−H···

N = 2.669(11) Å, ∠N−H−N = 171.4°] between triazole

groups and between the thiourea NH of a protonated and a

triazole N of a neutral L6 [N−H···N = 2.970(7)Å, ∠N−H−N

= 166.84°]. Hydrogen bonds for 9 and 10 are reported in the

Supporting Information.

{[Hg₂(μ₃-L5′)I₃]}_∝(11). The reaction of the allyl-substituted

thiourea−triazole ligand L5 with HgI₂resulted in block-shaped

colorless single crystals of 11. SC-XRD analysis revealed that

crystals of 11 belong to the centrosymmetric monoclinic space

group P2₁/c (Table S1). Surprisingly, no L5 was detected in

the asymmetric unit. Instead, a ﬁve-membered cyclic derivative

of the 1,2,4-triazole ligand (5-ethyl-1-(4H-1,2,4-triazol-4-yl)-

imidazolidine-2-thione, L5′) coordinated to two Hg metal

centers, was present, forming a 1D coordination polymer.

Three coordinated iodide anions complete the asymmetric

unit. The formation of L5′ is presumably due to a two-step

cyclization process in which L5 reacted with HgI₂to form a

complex in the initial step, and further nucleophilic attack of

[HgI]⁺on the allylic group (Hg−C bond) resulted in L5′. The

proposed mechanism of the cyclization process is shown in

Scheme S1. The four coordinated Hg(II) metal center shows a

distorted trigonal pyramidal geometry (τ₄= 0.78), with two

iodine atoms and a thiourea S atom at the equatorial positions

Photoluminescent Properties. Emission and excitation

spectra of compounds 1−11, as well as those of corresponding

organic ligands, L1−L6 were investigated in the solid state.

Figure 13. Crystal structure illustration of 11. (a) Extended

asymmetric unit showing the trigonal pyramidal and linear geometry

around the Hg atoms, as well as coordination of L5′; (b) 1D zigzag

CP along the 2₁-axis.

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Under UV−vis light excitation at room temperature, none of

these samples exhibit a distinct photoluminescent signal. This

is in contrast with the previously reported series of d¹⁰-metal

(Zn(II), Cd(II), Hg(II)) complexes and the related coordina-

tion polymers bearing 1,2,4-triazole-based ligands substituted

at the 4-position with phenyl-containing groups.⁵¹In the

reported case, both free organic ligands as well as the

subsequent coordination compounds showed room temper-

ature blue to blue-green photoluminescence originating from

diverse emissive states, mainly related to ligand-centered

electronic transitions. This can be correlated herein with the

structure of L1−L6 ligands which also contain 1,2,4-triazole

groups, but the remaining organic parts do not contain the

aromatic rings, which could result either in larger π-conjugated

moieties leading to strongly emissive intraligand charge

transfer (ILCT) states or in the appearance of emissive

ligand-to-ligand charge transfer (LLCT) states occurring

thanks to the favorable supramolecular arrangement of ligands

neighboring in the crystal lattice. Despite these limitations, a

distinct photoluminescence was however detected for com-

pounds 7, 10, and 11 which all contain binuclear units, as well

as in the corresponding free organic ligands, L5 and L6, after

cooling the samples to 77 K (Figures 14, 15, and 16).

Under UV light excitation, compound 7 exhibits broad

emission centered at λ = 420 nm with a shoulder around λ =

520 nm (Figure 14, Table S6). This luminescence is

hypsochromically shifted when compared with the free ligand

L5 showing the broad emission bands at λ = 450 nm or λ =

518 nm, depending on the excitation wavelength (Figure 14,

Table S6). The ligand L5 is built of the 1,2,4-triazole group

substituted at the 4-position with the thiourea moiety ﬁnishing

with the well-separated terminal allyl group (Scheme 2). Thus,

the occurrence of the ILCT states can be rather excluded.

Moreover, the crystal structure of L5 (Figure 3) does not

suggest the formation of supramolecular aggregates involving

aromatic 1,2,4-triazole groups which could lead to the LLCT

emission. Therefore, the observed photoluminescence of L5

can be attributed to the classical ligand-centered (LC)

ﬂuorescence involving mainly the triazole π-electron system

only modulated by the complex substituent. The typical UV

excitation of L5 at λ = 370 nm produces green emission related

to the broadband centered at λ = 520 nm, while the deeper UV

light of λ = 270 nm results in another emission band with the

maximum at ca. λ = 450 nm. These emission signals can be

ascribed to two diﬀerent isolated LC states as clearly visible in

two distinguishable bands in the excitation spectrum. A similar

excitation pattern was observed for the analogous ligand of N-

(1,2,4-triazol-4-yl)pyridine-3-carboxamide bearing aromatic

triazole and pyridine moieties well separated by the

carboxamide group.⁵¹Such a two-maxima character of the

excitation spectrum remains after the coordination of L5 by

Hg(II) metal centers within the 2D coordination polymer of 7.

Therefore, the resulting emission of 7 can be assigned to the

LC transitions as the formation of supramolecular aggregates

of L5 ligands, which could lead to the emissive LLCT states, is

not observed in the crystal structure of this coordination

network (Figure 11). Both the excitation bands as well as the

resulting emission signals of 7 are signiﬁcantly blue-shifted

when compared with free ligand L5 (Figure 14). It can be

explained by the strong conformational modiﬁcation of the

ligand upon metal coordination as well as the generation of the

deprotonated form of L5⁻, which balances the positive charge

of Hg(II) metal centers.⁶⁷As a result, the CIE 1931

Figure 14. (a) Solid-state photoluminescence of 7 and (b) the free

ligand L5 presented through emission spectra for the indicated

excitation wavelengths and excitation spectra for the indicated

monitored emission wavelengths. All spectra were gathered at 77 K.

chromaticity parameters of the ligand L5 emission of (0.228,

0.494) dramatically change to (0.215, 0.216) for the

luminescent signal of 7 ,which gives the emission color shift

from green to blue (Figure S1 and Table S6). Despite the

strong suggestions of the LC origin of the emission in 7, one

cannot exclude the contribution of the ligand-to-metal charge

transfer (LMCT) states which are accessible for Hg(II)

complexes.^68,69

The clariﬁcation of the emission mechanism in 7 is enabled

by the theoretical calculations of the electronic densities of

states (Figure 19b, see next section). The highest occupied

states are mainly assignable to the LC electronic states. On the

contrary, the lowest unoccupied states contain the main

contribution from the ligand states; however, there is a non-

negligible contribution from the Hg(II) electronic states.

Therefore, the lowest energy optical transition, which is

responsible for the observed emission pattern, can be described

as a mixture of LC and LMCT (L5 to Hg(II)) transitions. This

assignment explains also the observation of a few overlapping

emission components at ca. λ = 400, 450, and 540 nm,

accompanied by the tail toward higher wavelengths (Figure

14).

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light irradiation at λ = 275 nm, which results in the broad

emission band ranging from ca. λ = 350 to 600 nm, with the

maximum in the blue region of the spectrum, at λ = 455 nm.

Similarly to 7, the emission of 10 is also hypsochromically

shifted when compared with the free ligand L6 exhibiting

green photoluminescence with the broad emission band

centered at λ = 530 nm (Table S6). The related xy CIE

1931 chromaticity parameters change from yellowish green

(0.331, 0.445) for the free ligand to blue (0.219, 0.241)

(Figure S1, Table S6). The ligand L6 contains only a single

aromatic group of 1,2,4-triazole substituted with long aliphatic

tail involving the thiourea-ethyl(acetate) moiety (Scheme 2),

and its crystal packing does not suggest the formation of any

speciﬁc supramolecular aggregates (Figure 4). The ILCT or

LLCT emissive states are, then, rather excluded, and the

observed emission of L6 can be assigned to LC ﬂuorescence.

Both the excitation as well as the emission patterns are shifted

going from free ligand L6 to 10, which indicates the blue-

shifted emission of a similar LC ﬂuorescent origin. The blue-

shift can be explained by the signiﬁcant molecular reorientation

of L6 molecules upon metal coordination in 10 (Figure 15).

There is a lack of ligand-based supramolecular stacks within

the crystal structure of 10, which could have suggested the

appearance of some additional emissive LLCT states.

However, the other possible sources of emission in 10,

including the charge transfer states between iodide ion and

Hg(II) centers (halide-to-metal charge transfer, XMCT),

between iodide and ligand L6 (halide-to-ligand charge transfer,

XLCT), or between ligand L6 and Hg(II) centers (ligand-to-

metal charge transfer, LMCT), cannot be easily excluded, as all

are accessible for the family of Hg(II) halides with aromatic

heterocyclic ligands.^34,46,47

The clariﬁcation of the emission origin in 10 is also provided

by the theoretical calculations of the electronic densities of

states (Figure 19b, see next section). The highest occupied

states are of a predominant ligand character; in particular, the S

atoms of ligand L6 contribute the most to these states. On the

contrary, the lowest unoccupied states are of the mixed L6 and

Hg(II) character, indicating that the lowest energy optical

transitions can be mainly described as the combination of LC

and LMCT (L6 to Hg(II)) transitions. Therefore, the

emission of 10 can be assigned to the combined contributions

from LC and LMCT transitions which agrees well with the

observed broad emission patterns visibly consisting of a few

overlapping components at ca. λ = 380, 450, and 530 nm, even

with the tail toward higher wavelengths (Figure 15). One

additional remark should be given to the role of iodide ions

which bridge two Hg(II) centers within the dinuclear

molecules of 10 (Figure 12). In the calculated DOS, there is

a signiﬁcant contribution from iodide ions in the energy states

very near the highest occupied states, suggesting that there

should be also a nonzero contribution from the halide-related

XMCT/XLCT states to the overall emission. This interpreta-

tion becomes even more probable when noticing that the

analogous isostructural compounds 8 and 9, containing

chloride and bromide ions, respectively, do not exhibit the

emission even at 77 K. The calculated DOS of 8 (Figure S13)

indicates that the characters of lowest unoccupied, as well as

highest occupied states, remain similar in comparison to 10

(Figure 19b, see next section). However, the contribution of

chloride-related states is positioned well below the highest

occupied state, which reveals almost a purely ligand-based

character. Besides, the lowest unoccupied states in 8, which are

Figure 15. (a) Solid-state photoluminescence of 10 and (b) the free

ligand L6 presented through emission spectra for the indicated

excitation wavelengths and excitation spectra for the indicated

monitored emission wavelengths. All spectra were gathered at 77 K.

Figure 16. Solid-state photoluminescence of 11 presented through

emission spectra for the indicated excitation wavelengths and

excitation spectrum for the indicated monitored emission wavelength.

All spectra were gathered at 77 K.

The UV-light-induced visible photoluminescence is also

observed for {Hg(II)₂} dinuclear molecules of 10 (Figure 15).

The distinct emission signal was detected under the deep UV

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still of a mixed Hg/L6 character, are split into two distinct

parts. These modiﬁcations are expected to play an important

role in the observed experimental diﬀerences, the lack of

detectable emission in 8 and 9 with the presence of a distinct

emission signal in 10.

has been shown in many cases, wherein the conformation of

both the free ligand (before reacting with metal ion) and the

coordination compound (of the same ligand) showed

diﬀerences.^72,73Interestingly, ﬂexible ligands which have

various plausible conformations are the key factors for

successful self-assembly of important supramolecular com-

pounds such as polycatenanes,⁷⁴helices,^75,76braids,⁷⁷

Borromean rings,⁷⁸2D square grids,⁵single-walled metal−

organic nanotube,⁶and so on. However, it is a diﬃcult task to

predict the crystal structure of a coordination compound built

from a ﬂexible ligand due to (i) various possible conformations

and coordination modes of these ligands; (ii) the diﬃculty to

precisely determine their energies; and (iii) the kinetic and

thermodynamic factors for the stability of the complexes and

the crystal packing eﬀect. In order to understand and precisely

determine the ﬁnal topological structure of the CPs, often the

molecular level building block approach or a crystal engineer-

ing approach is used, in which the building blocks [supra-

Visible light emission is also observed for compound 11

(Figure 16). Under UV-to-blue light excitation, it reveals an

emission band centered at ca. λ = 540 nm, which results in the

green photoluminescence characterized by the (0.296, 0.550)

xy CIE 1931 chromaticity parameters. This is a noticeably

lower energy emission in comparison to the other investigated

compounds 7 and 10 (Table S6), even though the similar

structure of the organic ligand, L5′, which is spontaneously

formed from ligand L5, undergoes cyclization during the

crystallization process (Scheme S1). This ligand is only

observed in the crystal structure of 11 and could not be

isolated separately. Thus, its emission properties could not be

determined. However, similar to other investigated ligands, it

consists of the aromatic 1,2,4-triazole group with the 4-position

substituent composed of an aliphatic ring with an additional

thiocarbonyl group. Because of the lack of a large π-conjugated

system, this ligand is not expected to exhibit any IL-charge-

transfer transitions. In the crystal structure of 11, there are no

speciﬁc supramolecular aggregates of the ligand which could

lead to the related LLCT emission. Therefore, the observed

emission in 11 can be either the result of the LC ﬂuorescence

or the CT emission involving Hg(II) metal centers and organic

ligand (LMCT). Alternatively, the CT emission related to the

presence of iodide anions coordinated to Hg(II) centers, being

also in the proximity of organic ligands (possible XMCT and

XLCT states), could also be considered. The indication, on

which emission pathway is realized in compound 11, is given

by the theoretical calculations of the electronic densities of

states (Figure 19b, see next section). The highest occupied

state was found to be mostly of a halide character, which is

very diﬀerent from results found for compounds 7 and 10 (see

above). On the contrary, the lowest unoccupied state is

strongly mixed, having both large contributions from Hg(II)

metal centers (predominant one) as well as organic ligands

focused mainly on the C/N-based rings rather than S atoms.

As a result, the lowest energy optical transition is of XMCT

and XLCT character. This indicates that the XMCT/XLCT

origin of the emission property in 11 diﬀers signiﬁcantly

compared to previously discussed 7 and 10 where LC and

LMCT emissive transitions dominated. A similar XLCT

emission was reported for the related Hg(II)-based complexes

involving the simultaneous coordination of bromide anions

and other triazole-containing ligands, N-(1,2,4-triazol-4-yl)-

pyridine-3-carboxamide.³⁴In that case, similarly to 11, the

resulting emission appears thanks to the appropriate supra-

molecular arrangement of halide ions in close vicinity of

triazole-based ligands accompanying the direct coordination to

Hg(II) centers. Besides, it seems that such XLCT/XMCT

transitions can produce a longer wavelength emission in

comparison to the LC/LMCT emissive state found in 7 and

10.

molecular synthons^79,80/secondary building units (SBUs)^81,82

]

are capable of making predictable motifs within the resultant

crystal structure.

In this work, we designed and synthesize a series of new

ligands based on a thiourea backbone with 1,2,4 triazole

functional groups on one side and alkyl, allyl, or ester

functional groups on the other side, namely, L1−L6, as well as

a polymorph of L4 and a MeOH solvate of L6 (Scheme 2).

The ligand exhibits a degree of free rotation around the N−N

bond connecting the 1,2,4-triazole and thiourea moieties

(N_{1,2,4‑triazole}−N_thiourea), and four extreme conformers can be

generated by rotation around the C−N bonds within the

thiourea fragment, denoted as syn−anti, syn−syn, anti−syn, and

anti−anti (Scheme 3).

All ligand structures crystallize in centrosymmetric space

groups forming a hydrogen bonded homosynthon over the

2

inversion center. In L2, L3, and L4, this R₂(8) ring structure is

formed between the NH adjacent to the triazole moiety and

the thiourea sulfur. All ligands are found in the syn-anti

conformation (Scheme 4). L1 and L5 also form a similar

2

R₂(8) ring structure, yet involving the other thiourea NH and

with the ligands in the anti-syn conﬁguration. For L1, this

situation results from the interaction with the lattice water

molecule, whereas for L5 this is the result of packing

interactions. This ﬁts very well with theoretical calculations

showing that relative energies between the diﬀerent con-

formations are quite small (see next section). In L6, a

bifurcated hydrogen bond engaged in intra- and intermolecular

interactions with the carbonyl oxygen of the ester group is

observed rather than thiocarbonyl. This also imposes the anti-

syn conﬁguration. In all structures, the 1,2,4-triazole group is

oriented almost perpendicular (83.35−86.16°) to the thiourea

(Figure 17).

Although metal complexes with thiourea moieties are not

uncommon (>1300 crystal structures recorded in the CSD),⁴²

only 64 complexes involve a mercury complex, and even fewer

complexes (>50) are reported between mercury and a triazole

ring. Moreover, only two ligands with the 1,2,4-triazole group

directly attached to the thiourea moiety via an N−N bond are

known⁵⁵and none as a metal complex.

DISCUSSION

■

In all of our complexes, complexation with the Hg(II) atom

occurs through the thiourea sulfur, with an oﬀset angle Hg···

SC of 102.6° on average (range 96.6−109.9°), which is

consistent with the CSD database (average 101.6° 5.6). The

1,2,4-triazole moiety is in general found on opposite sides of

The conformation of the ligand is, naturally, one of the

important factors which aﬀects the crystal structure of a

complex, but the nature of the central metal ions, and

counteranions are rather the decision making factors for the

conformation of ligands in coordination compounds.^70,71This

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Figure 18. Overlay of ligand conformations as observed in the

corresponding complexes (shown in green with the Hg atom as blue)

and free ligand (shown in red color). (a) L1 and 1; (b) L1 and 2 (the

water molecule in the free ligand is also shown); (c) L2 and 3; (d) L3

and 4; (e) L4 and 5; (f) L4 and 6; (g) L5 and 7; (h) L6 and 8

(superposition of L6 on both the neutral and deprotonated ligand of 8

are shown).

Figure 17. Stick representation of the homosynthons formed in L1−

L6.

scope of a continuum solvation approximation (Figure 19a). It

can be seen that, overall, all conformations of L1 and L4 have

competitive stabilities, all lying within a 3 kcal/mol range. In

the case of L1 (anti-syn), the strength of, as an example, the

nearest-neighbor triazole···H₂O interaction is computed to be

−7.7 kcal/mol; this corroborates that the collection of

intermolecular interactions in a given crystal can “override”

the small stability diﬀerences between the free ligand

conformers. L6, on the other hand, stands out because of its

particularly stable anti-syn conformation; this preference comes

from the ability to create an intramolecular hydrogen bond

between the thiourea N−H and carbonyl CO groups. In the

case of L6, the (most stable) anti-syn conformation is that

which appears in the L6 crystal structure. When the thiourea

N−H proton of L6 is moved to the 1,2,4-triazole ring (labeled

L6′), the strong conformational preference for anti-syn is lost

because of the lack of an intramolecular hydrogen bond, and

the L6′ anti-anti conformation becomes competitive; the anti-

anti and anti-syn conformations are the two conformers which

are adopted in the structures 8−10. Thus, in complexes 8−10,

the preferred conformers of the free ligand are also arguably

preserved. As is discussed below, for every functional group

(including L6) the scale of the intermolecular interactions is

much larger than the energy diﬀerences between conformers,

but the set of ligands we chose successfully maps out a rich

structural space in which the conformational preferences of the

ligand are sometimes preserved (in the case of L6, albeit with

deprotonation being a decisive factor in the CP structures) and

sometimes composition-dependent (in the cases of L1 and

L4).

the triazole sulfur to minimize repulsion (syn-anti, Scheme 2);

nevertheless, the diﬀerent conformations are very close in

energy (see next section) and can easily convert into each

other. Upon deprotonation or proton transfer from the triazole

NH to the triazole ring the other conﬁguration is observed

(anti-syn or anti-anti, Scheme 2). Deprotonation allows

additional coordination through the triazole moiety and the

formation of coordination polymers, as observed for instance

in 4 and 7. The syn-syn conﬁguration is not observed among

the current series. Deprotonation or proton transfer also

inﬂuences the coordination mode of the Hg center. A striking

example is the diﬀerence between complexes 5 and 6, both

built from ligands L4. In 6, charge neutrality is achieved by two

iodine anions, forming a tetrahedrally coordinated binuclear

complex, while in 5 only one chlorine anion is necessary,

resulting in a trigonal complex. It is as yet unclear how the

deprotonation of the ligands is achieved, as all complexes were

produced in similar manner by mixing the starting salt and

ligand in an equimolar ratio and crystallizing the complexes by

either evaporation or convection, without any method

systematically leading to deprotonation.

In Figure 18, the ligands in their free form and complexed to

mercury are superposed by ﬁtting the thiourea moieties onto

each other, which also demonstrates why the syn-syn

conﬁguration is not observed as this would bring the triazole

and alkyl ends too close to each other. More details about the

coordination modes of the ligands and the corresponding bond

lengths in compounds 1−10 are shown in Table S3. The alkyl

end of the ligand has little inﬂuence on the coordination mode

or type of the formed complexes, not even for ligand L6, where

the free ligand shows inter- and intramolecular hydrogen

bonding through the carbonyl oxygen.

One of the important factors which determines the

supramolecular architectures of coordination compounds is

the presence of hydrogen bonding in the ligand molecule. A

design strategy based on the combination of both metal to

ligand coordination bonding and hydrogen bonding in

designing various metal organic supramolecular architectures

is an established area of research. Interestingly, this strategy

attracted many materials chemists due to the probability of

To investigate the inﬂuence of the ligand conformation, the

relative stabilities of four diﬀerent conformations of L1, L4,

and L6 as depicted in Scheme 2 were calculated by DFT, with

solvation eﬀects considered from dichloromethane within the

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chain structure as the primary supramolecular structure, which

is further extended to a 2D hydrogen bonded sheet through

C−H···S and N−H···S hydrogen bonding involving thiourea

and lattice included DMSO molecules. A similar kind of

supramolecular structure is found in the crystal structure of 6;

the only diﬀerence is a lattice included solvent, DMSO in 2

and MeOH in 6.

While ligand L2 showed N−H···N and N−H···S hydrogen

bonding involving the triazole and thiourea which resulted in

the formation of a 1D zigzag chain, 3 derived from L2

exhibited thiourea···triazole hydrogen bonding (N−H···N),

and π···π stacking interactions (between triazole rings) resulted

in 2D corrugated hydrogen bonded sheet structure, which

further self-assembled to a 3D hydrogen bonded network with

the support of N−H···O hydrogen bonding involving lattice

included MeOH with thiourea and triazole moieties of the

adjacent sheets. The ligands L3 and L4 also showed a similar

type of hydrogen bonding and a 1D zigzag chain structure like

L2. The 2D square grid 4 built from L3, having a corrugated

sheet-like architecture, is stabilized by N−H···N intramolecular

hydrogen bonding interaction, and such sheets are further self-

assembled on top of each other with the support of weak van

der Waals interactions. A similar type of hydrogen bonding and

packing is observed in 7. However, the ligand L5 used for the

synthesis of 7 showed thiourea ···triazole interaction through

N−H···N and N−H···S hydrogen bonding and led to the

formation of a 1D zigzag chain, which is the primary

supramolecular synthon. These chains are further assembled

into a 2D hydrogen bonded corrugated sheet having a

hexagonal grid topology via self-complementary thiourea···

thiourea hydrogen bonding. 5 self-assembled to form a

macrocycle via N···N interaction between two triazole

moieties. Moreover, other supramolecular interactions such

as C−H···Cl, C−H···π, and π···π stacking, involving isopropyl

C−H with metal bound Cl, triazole C−H with a triazole ring,

and thiourea CS with a triazole ring, respectively, resulted in

the formation of an oval-shaped microporous supramolecular

structure. However, the inclusion of MeOH molecules blocked

such pores. The self-assembly of isomorphous crystals of 8, 9,

and 10 through N−H···N hydrogen bonding involving the

protonated form of triazole, thiourea, and neutral triazole

functionalities, resulted in the formation of a 3D hydrogen

bonded network structure.

In order to provide physical insight into factors contributing

to the stability of the reported species, extensive bonding

analyses based on both cluster and periodic calculations were

performed (Figures S5 −S13). We shall not discuss these data

in detail but provide herein only the most relevant ﬁndings. A

more detailed discussion is provided in Supporting Informa-

tion. First of all, ETS-NOCV data have revealed that London

dispersion forces are indispensable for the overall ligand

stability − ΔE_dispcovers ∼80% of the overall stabilization in

L4, 68% in L3 (CH···S, CH···π, CH···HC), 51% in L1 (CH···

S, π···π), 48% in L6 (σ-hole···π, NH···N), 42% in L5 (CH···N,

CH···π), and 38% in L2 (CH···π), Figures S5 −S10. As far as

the corresponding metal polymers are concerned, one shall

state that although dative-covalent [due to two-way electrons

transfer: Lp(6s/5p, Hg) → σ*(SC) and Lp(S) → σ*(Hg−

I/S)] and electrostatically dominated Hg−S bonds are

quantitatively of prime importance, they are supported by a

bunch of unclassical mostly London dispersion driven

noncovalent interactions, including for example: CH···π,

π···π, CH···I, and CH···HC (Figure S13); particularly, the

Figure 19. (a) Relative total DFT energies of the ligand conformers

deﬁned in Scheme 2; shown are L1, L4, L6, and L6′, where L6′ was

built from L6 by moving a proton from the thiourea subunit to the

triazole subunit. (b) Computed electronic densities of states (black

line) for 6, 7, 10, and 11 with the PBE+D3 functional; also shown, as

indicated in the legend, are the atom-projected contributions to the

total DOS, wherein the ligand contribution (i.e., L4/L5/L6)

corresponds to the sum of all the atoms in the ligand. The Fermi

energy is set to zero, and note that 11 does not contain L5 (as

described in the text).

structural diversities, guest entrapment supported by hydrogen

bonding interactions, and functional properties having

potential applications. The important beneﬁt of using a

hydrogen bonding capable ligand for the synthesis of

complexes is their ability to form interchain or internetwork

hydrogen bonding. The resulting materials show intriguing

supramolecular structures and robustness in their framework.

Thiourea is a well-known hydrogen bonding capable functional

group, used in supramolecular and coordination chemistry.^83,84

The ligands (L1−L6) contain hydrogen bonding capable

groups such as thiourea, 1,2,4-triazole, and alkyl, allyl, or ester

functional units. More details of hydrogen bonding of various

functionalities of ligands and solvent molecules are shown in

Table S2. The molecules of ligand L1 in its free form, interact

with each other through lattice included water molecules, via

N−H···O, N−H···S, O−H···N, and C−H···S hydrogen

bonding involving thiourea, triazole, and methyl moieties,

resulting in a 2D hydrogen bonded supramolecular network.

Because of the anti-syn conformation of ligand L1, thiourea···

thiourea self-complementary hydrogen bonds (N−H···S) are

absent in the crystal structure. On the other hand, the N−H···

N hydrogen bonding (thiourea···triazole) in 1 resulted in a 3D

network; 2 undergoes self-assembly through thiourea···triazole

hydrogen bonding (N−H···N), and π···π stacking between the

triazole rings leads to the formation of a 1D hydrogen bonded

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latter ones are intriguing and recently under extensive debate

due to a real understanding of steric-crowding in small and

sizable species⁸⁵⁻⁸⁸(Figures S12 −S13). The varying motifs

that are observed as a result of the self-assemblies in 1−11 also

result, as could be expected, in distinct valence and conduction

band electronic structures, as demonstrated in Figure 19b with

6, 7, 10, and 11. The colored bars indicate the atoms in the

coordination sphere of Hg which dominantly contribute to

valence and conduction band energy levels, and they can be

seen to change in both atom-type and length. Also, the makeup

of the highest occupied energy levels varies considerably,

progressing from halide-based in 6 to thiolate-character in 10

and signiﬁcant triazole-character in 7. It should be noted that

the particulars of the electronic structure are sensitive the level

of theory that is used (for example, the use of hybrid DFT

functionals or the inclusion of spin−orbit relativistic eﬀects),

but the results clearly show that a broad distribution of self-

assembled building blocks and of electronic structures is

successfully realized.

of various nonbonded interactions. One-dimensional zigzag CP

11 self-assembled with the support of various supramolecular

interactions and led to the formation of a 3D hydrogen bonded

network structure, embedding a new ligand formed in situ.

Among the series, 7, 10, and 11 were found to exhibit UV-

light-induced photoluminescence in the visible range. They

show the great potential of mercury(II)-halide coordination

systems bearing 1,2,4-triazole derivatives in the generation of

multicolored luminescence originating from remarkably diverse

emissive electronic states, ranging from ligand-centered

ﬂuorescence modiﬁed upon ligand coordination and combined

with organic-ligand-to-metal charge transfer (7 and 10), as well

as halide-to-metal-charge transfer emission related to the d¹⁰

electronic conﬁguration of Hg(II), combined with halide-to-

ligand charge transfer taking advantage of the appropriate

arrangement of organic ligands and halide ions (11). The

origin of the emission transitions was elucidated on the basis of

experimental observations compared with the emission

patterns of the respective organic ligands, with the critical

support of theoretical calculations of the electronic densities of

states. Interestingly, all emission eﬀects were achieved in 7, 10,

and 11 by using relatively small 1,2,4-triazole derivatives

incorporating rather short substituents in comparison to the

previously reported Hg compounds with sterically expanded

derivatives bearing phenyl moieties giving large π-conjugated

systems and the related intraligand or ligand-to-ligand charge

transfer emissive states.²⁹It indicates that the reported Hg(II)

halides incorporating ﬂexible triazole-based ligands form a

promising class of luminescent molecular materials oﬀering a

remarkably rich diversity of accessible and often coexisting

emissive states which could be further explored toward eﬃcient

dual emissive states for applications in luminescent sensors or

ratiometric luminescent thermometers. This study is also

important given that several laboratories, including our team,⁸⁹

are currently designing hybrid materials including such ligands

to capture Hg from aquatic media. It will help these researchers

to understand the performances of their materials and improve

their materials.

CONCLUSIONS

■

In this work, we have explored a series of novel triazole-

thiourea based ligands L1−L6 and their coordination and

hydrogen bonded self-assembly with Hg(II), which resulted in

two mononuclear complexes 1 and 5, ﬁve binuclear complexes

2, 6, 8, 9, and 10, and four coordination polymers 3, 4, 7, and

11. The SC-XRD analysis of these complexes revealed that

their coordination or hydrogen bonding dimensionality,

topology, and supramolecular structure depend on various

parameters such as conformation of ligands, counteranions,

hydrogen bonding present in the ligand, and supramolecular

interactions. While the self-assembly of triazole-thiourea

ligands having the substituents methyl, allyl, and ethyl ester

such as L1, L5, and L6, respectively showed a 2D hydrogen

bonded corrugated sheet structure, the triazole-thiourea

ligands with ethyl, propyl, and isopropyl moieties such as L2,

L3, and L4 resulted in 1D zigzag hydrogen bonded chains. All

of these ligands showed thiourea···thiourea (N−H_(TU)···S_(TU)

)

hydrogen bonding, and also other supramolecular interactions

involving thiourea, triazole, and other functional groups. The

ligands showed anti-syn and syn-anti conformations, when they

packed into a 2D hydrogen bonded sheet and 1D chains,

respectively.

The supramolecular assembly of 1 with the support of

thiourea···triazole (N−H_(TU)···N_(TZ)) interaction leads to the

formation of a 3D hydrogen bonded network structure. The

supramolecular structure of 2 is a 2D hydrogen bonded sheet

supported with thiourea···triazole, and thiourea···DMSO.

Binuclear complex 6 also has the same supramolecular

structure as 2, the only diﬀerence being the solvent of

crystallization. The self-assembly of mononuclear complex 5,

initially resulted in a macrocycle, which further interacts with

each other to form a 1D hydrogen bonded chain architecture,

EXPERIMENTAL SECTION

■

Materials and Characterization Methods. All solvents were

obtained from commercial sources. HgBr₂, HgI₂, Hg(NCS)₂, methyl

thiocyanate, and allyl isothiocyanate were provided from Acros

Organics. HgCl₂and ethyl thiocyanate were obtained from Sigma-

Aldrich. Propyl isothiocyanate, isopropyl isothiocyanate, and ethoxy

carbonyl isothiocyanate were provided from TCI Chemicals. ¹H

NMR spectra were recorded at 300 MHz on a Bruker AC300

instrument by using DMSO-d₆solvent, with tetramethylsilane (TMS)

as an internal standard at ambient temperature. High resolution mass

spectral data were recorded in methanol on a Thermo Finnigan LCQ

ion trap spectrometer in ESI mode, detecting positive ions. FT-IR

spectra were recorded on a PerkinElmer 1310 spectrometer in the

range 400−4000 cm⁻¹using KBr pellets. CHN analyses were

performed at MEDAC Ltd.

containing “I”-shaped subunits, sustained by N−H_(TZ)···N_(TZ)

.

Diﬀuse reﬂectance spectra were obtained with a PerkinElmer

Lambda 9 UV/vis/NIR spectrophotometer equipped with a 60 mm

integrating sphere and converted into absorption spectra by using the

Kubelka−Munk function, using BaSO₄as a reference. Powder X-ray

diﬀraction patterns were recorded on a Siemens D5000 counter

diﬀractometer working with a Cu K_αradiation (λ = 1.5148 Å) at 293

K. Photoluminescent characteristics, including solid-state emission

and excitation spectra at room temperature as well as liquid nitrogen

temperature, were investigated using an FS5 spectroﬂuorometer

(Edinburgh Instruments) equipped with a Xe (150 W) arc lamp as an

excitation source and a Hamamatsu photomultiplier of the R928P

8, 9, and 10 turned out to be isomorphous crystals and self-

assembled into a 3D hydrogen bonded network structure

supported by thiourea···thiourea (N−H_(TU)···S_(TU)), triazole···

triazole (N−H_(TZ)···N_(TZ)), and thiourea···triazole (N−H_(TU)···

N

_(TZ)). The 2D square grid 4 and 7 undergo thiourea···triazole

(N−H_(TU)···N_(TZ)) hydrogen bonding interactions and re-

sulted in the extension of the dimensionality from 2D CP to

3D structure. The 1D CP 3 extended its self-assembly to a 2D

hydrogen bonded corrugated sheet structure, with the support

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type as a detector. During these studies, the solid samples of ligands

L1−L6 as well as compounds 1−11 were measured in the form of a

well-ground powder placed at the bottom of a natural quartz tube,

which was inserted in the liquid nitrogen dewar mounted in the

sample chamber of the spectroﬂuorometer. Background corrections

were performed within the Fluoracle software (Edinburgh Instru-

ments).

Syntheses. Synthesis of Thiourea-Triazole Ligands L1−L6.

Equimolar amounts of 4-amino-1,2,4-triazole and isothiocyanate

derivatives were dissolved in ethanol (25 mL) in a 100 mL round-

bottom ﬂask. The mixture was reﬂuxed for 24 h at 60−75 °C,

resulting in a pale yellow clear solution. The solution was left to cool

at room temperature, and a white precipitate was collected by

ﬁltration. This product was washed with water (30 mL) and puriﬁed

by recrystallization from methanol (20 mL) to obtain white crystals.

The crystals were ﬁltered, washed with ether, dried in air, and kept in

a desiccator over silica gel.

and THF (3 mL). The mixture was stirred for 4 h at room

temperature to yield to a turbid solution which was ﬁltrated, yielding

to a clear solution which was left for slow evaporation. Plate cubic

colorless crystals were ﬁltered oﬀ after 4 days, washed with methanol

(3 mL), dried under a vacuum, and transferred into brown bottles to

prevent light exposure. Yield: (26 mg) 52%. Mp.: ∼170 °C. ¹H NMR

(300 MHz, DMSO-d₆): δ, 11.81 (br, s, 1H, NH), 10.83 (br, s, 1H,

NH), 8.65 (s, 2H CH of trz), 4.22 (q, 2H of CH₂), 1.27 (t, 3H of

CH₃). IR (cm⁻¹) 3242, 1719, 1252, 1105.

L6_MeOH-2. A total of 0.23 mmol of HgI₂(105 mg) and 0.23

mmol of L6 (50 mg) were placed in the main arm of a Γ glass tube

(Figure S7) which was ﬁlled with methanol. While the main arm was

heated in an oil bath at 60 °C, colorless, block-shaped crystals

deposited on the cooler arm after 6 days. These were ﬁltered oﬀ,

washed with methanol (3 mL), and dried in air. Yield: (35 mg) 70.5%.

Mp.: ∼168 °C. ¹H NMR (300 MHz, DMSO-d₆): δ, 11.81 (br, s, 1H,

NH), 8.65 (s, 2H CH of trz), 4.26 (q, 2H of CH₂), 1.27 (t, 3H of

CH₃). IR (cm⁻¹) 3242, 1719, 1252, 1105.

Single crystals of L6 were obtained as follows: 0.51 mmol of HgCl₂

(140 mg) and 0.26 mmol of L6 (50 mg) were placed in the main arm

of a Γ glass tube which was ﬁlled with methanol. While the main arm

was heated in an oil bath at 60 °C, colorless, block-shaped crystals

deposited on the cooler arm after 3 days. These were ﬁltered oﬀ,

washed with methanol (3 mL), and dried in air. Yield: (40 mg) 71%.

Mp.: ∼166 °C. 1H NMR (300 MHz, DMSO-d₆): δ, 11.82 (br, s, 1H,

NH), 8.65 (s, 2H CH of trz), 4.26 (q, 2H of CH2), 1.26 (t, 3H of

CH₃). IR (cm⁻¹) 3325, 1819,1650, 1436, 1205, 650.

1-Methyl-3-(4H-1,2,4-triazol-4-yl) Thiourea (L1). Yield: (1.31 g)

1

75%. Mp: 208 °C. H NMR (300 MHz, DMSO-d₆): δ 10.75 (br, s,

1H, NH), 8.68 (s, 2H CH of trz), 8.33 (br, s, 1H, NH), 2.82 (d, 3H

of CH₃). Anal. Calc. for C₄H₇N₅S: C, 30.57.13; H, 4.49; N, 44.50%;

Found: C, 30.27; H, 4.36; N, 44.00%. IR (cm⁻¹) 3100, 1589, 1073,

614,755. MS (ESI): m/z 158.04959 [M + H]⁺.

1-Ethyl-3-(4H-1,2,4-triazol-4-yl) Thiourea (L2). Yield: (1.51 g)

1

74%. Mp.: 157 °C. H NMR (300 MHz, DMSO-d₆): δ 10.63 (br, s,

1H, NH), 8.66 (s, 2H CH of trz), 8.45 (br, s, 1H, NH), 3.46 (m, 2H

of CH₂), 1.11 (t, 3H of CH₃). IR (cm⁻¹) 3156, 2904, 1567, 1180,

1053, 743, 598. Elem. Anal. Calc. for C₄H₇N₅S: C, 34.90; H, 5.24; N,

41.39%; Found: C, 35.07; H, 5.03; N, 40.90%. MS (ESI): m/z

172.06514 [M + H]⁺.

Synthesis of Coordination Compounds. [Hg(L1)₂(L1⁻)₂]} (1). A

total of 0.32 mmol of L1 (50 mg) and 0.1 mmol of Hg(NCS)₂(34

mg) were placed in the main arm of a Γ glass tube which was ﬁlled

with methanol. While the main arm was heated in an oil bath at 60

°C, colorless, block-shaped crystals deposited on the cooler arm after

12 days. These were ﬁltered oﬀ, washed with methanol (3 mL), and

dried under a vacuum. Yield: (81 mg) 32%. Crystals color changed to

black when exposed to air and light after 4 days. Anal. Calc. for 1·

4MeOH·10H₂O (HgC₂₀H₆₀N₂₀O₁₄S₄): C, 21.19; H, 5.33; N, 24.71%;

Found: C, 20.94; H, 2.66; N, 24.68%. IR (KBr, cm⁻¹): 3300, 3145,

2800, 1630, 1500, 1420, 1350, 800.

{[(Hg)₂(L1)₂(μ₂-I)₂(I)₂]·DMSO} (2). A total of 0.23 mmol HgI₂(106

mg) and 0.31 mmol L1 (50 mg) were dissolved in a mixture of

methanol (6 mL) and DMSO (2 mL). The mixture was stirred for 4 h

at room temperature to yield to a turbid solution which was ﬁltrated,

yielding to a clear solution which was left for slow evaporation.

Colorless, block-shaped crystals which were obtained after 8 days,

were ﬁltered oﬀ, washed with methanol (3 mL), and dried in air.

Yield: (133 mg) 41%. Anal. Calc. for 2 (C₁₂H₂₆Hg₂I₄N₁₀O₂S₄): C,

10.45; H, 1.90; N, 10.15%; Found: C, 9.93; H, 1.98; N, 10.08%. IR

(KBr, cm⁻¹): 3240, 3010, 2850, 2900, 1622, 1550, 1350, 1260, 830.

{[HgI(L2)(μ₂-I)]·MeOH}_∝(3). A total of 0.32 mmol of HgI₂(147.5

mg) and 0.29 mmol of L2 (50 mg) were dissolved in a mixture of

methanol (6 mL) and THF (3 mL). The mixture was stirred for 4 h at

room temperature to yield to a turbid solution which was ﬁltrated,

yielding to a clear solution which was left for slow evaporation. Yellow

plate crystals which were obtained after 13 days were ﬁltered oﬀ,

washed with methanol (3 mL), and dried in air. Yield: (92 mg) 48%.

Anal. Calc. for 3·MeOH (C₇H₁₇HgI₂N₅O₂S): C, 12.19; H, 2.48; N,

10.15%; Found: C, 11.74; H, 2.25; N, 10.12%. IR (KBr, cm⁻¹): 3200,

3000, 2820, 1630, 1550, 1470, 1360, 720.

1-Propyl-3-(4H-1,2,4-triazol-4-yl) Thiourea (L3). Yield: (1.04 g)

1

47%. Mp: 159 °C. H NMR (300 MHz, DMSO-d₆): δ 10.59 (br, s,

1H, NH), 8.66 (s, 2H CH of trz), 8.48(br, s, 1H, NH), 3.42 (m, 2H

of CH₂), 1.56 (sxt, 2H of CH₂), 0.86(t, 3H of CH₃). IR (cm⁻¹) 3112,

1572, 1179, 736, 600. Anal. Calc. for C₄H₇N₅S: C, 38.90; H, 5.99; N,

17.31%. Found: C, 37.93; H, 5.97; N, 17.43%. MS (ESI): m/z

186.08079 [M + H]⁺.

1-Isopropyl-3-(4H-1,2,4-triazol-4-yl) Thiourea (L4). Yield (1.19 g)

1

54%. Mp: 162 °C. H NMR (300 MHz, DMSO-d₆): δ, 10,42 (br, s,

1H, NH), 8,63 (s, 2H CH of trz), 4.42 (br, s, 1H, NH), 4.39 (m, H,

CH), 1.14 (d, 6H of 2 CH₃). IR (cm⁻¹): 3055, 1591, 1040,742, 631.

Anal. Calc. for C₄H₇N₅S: C, 38.90; H, 5.97; N, 37.30%. Found: C,

38.61; H, 5.99; N, 36.48%. MS (ESI): m/z 186.08079 [M + H]⁺.

1-Allyl-3-(4H-1,2,4-triazol-4-yl) Thiourea (L5). Yield: (1.42 g)

65%. Mp: 111 °C. ¹H NMR (300 MHz, DMSO-d₆): δ, 10.74 (s, 1H,

NH), 8.68 (s, 2H CH of trz), 8.65 (br, s, 1H, NH), 5.84 (d, d, 1H of

CH), 5.79 (m, 2H of CH₂), 4.10 (br, s, 2H, CH₂). FT-IR (cm⁻¹)

3230, 3083, 1350, 1540, 1230, 1080, 588. Anal. Calc. for C₄H₇N₅S: C,

39.33; H, 4.72; N, 38.22%. Found: C, 38.22; H, 4.72; N, 38.02%. MS

(ESI): m/z 184.06514 [M + H]⁺

Ethyl 2-(4H-1,2,4-triazol-4-yl) Acetate Thiourea (L6). Yield: (1.80

g) 70%. Mp: 169 °C. ¹H NMR (300 MHz, DMSO-d₆): δ, 12.22 (br, s,

1H, NH), 10.83 (br, s, 1H, NH), 8.65 (s, 2H CH of trz), 4.23 (m, 2H

of CH₂), 1.29 (t, 3H of CH₃).IR (cm⁻¹) 3242, 1719, 1252, 1105.

Anal. Calc. for C₄H₇N₅S: C, 33.48; H, 4.21; N, 32.54%. Found: C,

+

33.03; H, 4.05; N, 32.12%.). MS (ESI): m/z 216.05497 [M + H] .

L4-poly. A total of 0.136 mmol of HgCl₂(37 mg) and 0.27 mmol

of L4 (50 mg) were dissolved in a mixture of ethanol (6 mL) and

THF (3 mL). The mixture was stirred for 4 h at room temperature to

yield to a turbid solution which was ﬁltrated, yielding to a clear

solution which was left for slow evaporation. Plate cubic colorless

crystals were ﬁltered oﬀ after 4 days, washed with ethanol (3 mL),

dried under a vacuum, and transferred into brown bottles to prevent

{[(Hg)₂(μ-L3⁻)₄]}_∝(4). A total of 0.27 mmol of L3 (50 mg) and

0.32 mmol of HgCl₂(73 mg) were placed in the main arm of a Γ glass

tube which was ﬁlled with methanol. While the main arm was heated

in an oil bath at 60 °C, colorless, block-shaped crystals deposited on

the cooler arm after 2 weeks. These were ﬁltered oﬀ, washed with

methanol (3 mL), and dried in an air vacuum. Yield: (53 mg) 17%.

Anal. Calc. for 4·6H₂O (C₂₄H₄₈Hg₂N₂₀O₆S₄): C, 23.21; H, 3.89; N,

22.55%; Found: C, 23.78; H, 3.89; N, 21.75%. IR (KBr, cm⁻¹): 3100,

3020, 2840, 1750, 1620, 1450, 1370, 1190, 890.

1

light exposure Yield: (42 mg) 83%. Mp.: ∼160 °C. H NMR (300

MHz, DMSO-d₆): δ, 10.41 (br, s, 1H, NH), 8.63 (s, 2H CH of trz),

8.42 (br, s, 1H, NH), 4.39 (t, 1H, CH), 3.47 (q, 2H CH₂of Ethanol)

1.13 (d, 6H of 2 CH₃). 1.06 (d, 3H CH₃of ethanol). IR (cm⁻¹):

3094, 1570, 1062, 746, 616.

{[HgCl(L4⁻)L4]·MeOH} (5). A total of 0.27 mmol of HgCl₂(74 mg)

and 0.27 mmol of L4 (50 mg) were dissolved in a mixture of

methanol (6 mL) and THF (3 mL). The mixture was stirred for 4 h at

L6_MeOH-1. A total of 0.23 mmol of 74 mg of Hg(NCS)₂and 0.23

mmol of L6 (50 mg) were dissolved in a mixture of methanol (6 mL)

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Cryst. Growth Des. 2021, 21, 3562−3581

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room temperature to yield to a turbid solution which was ﬁltrated,

yielding to a clear solution which was left for slow evaporation. Plate

colorless crystals were ﬁltered oﬀ after 8 days, washed with methanol

(3 mL) and dried in air. Yield: (48 mg) 30%. Anal. Calc. for 5·H₂O

(C₁₃H₂₆ClHgN₁₀O₂S₂): C, 23.85; H, 4.00; N, 21.40%; Found: C,

23.66; H, 3.48; N, 21.71%. IR (KBr, cm⁻¹): 3360, 3120, 2870, 1620,

1490, 1380, 1250, 870.

{[(Hg)₂(L4)₂(μ₂-I)₂(I)₂]·2MeOH} (6). A total of 0.27 mmol of HgI₂

(123 mg) and 0.27 mmol of L4 (50 mg) were dissolved in a mixture

of methanol (6 mL) and THF (3 mL). The mixture was stirred for 4

h at room temperature to yield to a turbid solution which was

ﬁltrated, yielding to a clear solution which was left for slow

evaporation. Yellow, block-shaped crystals were ﬁltered oﬀ after 4

days, washed with methanol (3 mL) and dried in air. Yield: (115 mg)

32% Anal. Calc. for 6 (C₁₄H₃₀Hg₂I₄N₁₀O₂S₂): C, 12.52; H, 2.25; N,

10.43%. Found: C, 12.62; H, 2.14; N, 10.41%. IR (KBr, cm⁻¹): 3350,

3060, 2750, 1670, 1580, 1430, 1340, 980.

image plate using Mo Kα (λ = 0.71069 Å) radiation. The crystals

were selected from the mother solution, mounted in inert oil, and for

some transferred to the cold gas stream for ﬂash cooling (L1, L5, L6-

MeOH-1, 8). The unit cell parameters were reﬁned using all the

collected spots after the integration process. The data were not

corrected for absorption, but the data collection mode partially takes

the absorption phenomena into account. The structures were solved

by direct methods and reﬁned by full-matrix least-squares on F²using

SHELXL97.^90,91All the non-hydrogen atoms were reﬁned with

anisotropic temperature factors. All the H atoms were localized by

Fourier diﬀerence and included in the reﬁnement with an isotropic

temperature factor.

Computational Details. All calculations were performed using

density functional theory (DFT) methods within either the Vienna

Ab-Initio Simulation Package (VASP),⁹²for PBE+D3^93,94models of

periodic networks, or the Amsterdam Density Functional 2016

(ADF2016)^95,96programs, for BLYP+D3 models of molecules and

molecular clusters. Further details are given in the Supporting

Information about the computational parameters, results from

selected periodic models with a hybrid DFT functional and with

spin−orbit relativistic eﬀects, and an in-depth discussion about the

ligands’ interaction energies.

{[(Hg)₂(μ₂-L5⁻)₄]}_∝(7). A total of 0.27 mmol of HgCl₂(63 mg) and

0.27 mmol of L5 (50 mg) were dissolved in a mixture of methanol (6

mL) and THF (3 mL). The mixture was stirred for 4 h at room

temperature to yield to a turbid solution which was ﬁltrated, yielding

to a clear solution which was left for slow evaporation. Colorless,

block-shaped crystals were ﬁltered oﬀ after 12 days, washed with

methanol (3 mL), dried under a vacuum, and transferred into brown

bottles to prevent light exposure. Yield: (117 mg) 38%. Anal. Calc. for

7·32H₂O (Hg₂C₂₄H₉₂N₂₀O₃₂S₄): C, 16.93; H, 5.45; N, 16.45%;

Found: C, 16.55. H, 2.02, N 16.43%. IR (KBr, cm⁻¹): 3100, 3020,

1600, 2760, 1530, 1420, 1250, 740.

ASSOCIATED CONTENT

■

sı

* Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.cgd.1c00352.

[Hg₂(μ₂-Cl)₂(L6⁻)₂(L6)₂]} (8). A total of 0.39 mmol of HgCl₂(106

mg) and 0.23 mmol of L6 (50 mg) were dissolved in a mixture of

methanol (6 mL) and THF (3 mL). The mixture was stirred for 4 h at

room temperature to yield to a turbid solution which was ﬁltrated,

yielding to a clear solution which was left for slow evaporation. Plate

colorless crystals were ﬁltered oﬀ after 10 days, washed with methanol

(3 mL), dried under a vacuum, and transferred into brown bottles to

prevent light exposure. Yield: (91 mg) 36%. Anal. Calc. for 8·MeOH

(C₂₅H₃₆Hg₂Cl₂N₂₀O₉S₄): C, 22.06; H, 2.67; N 20.58%; Found C,

22.30; H, 2.70; N 20.88%. IR (KBr, cm⁻¹): 3220, 3040, 2560, 1500,

1480, 1345, 1280, 750.

Overview of NMR, mass spectrometry, IR, UV−vis,

luminescence, reaction mechanism of 11, crystallo-

graphic and theoretical modeling data (PDF)

Accession Codes

CCDC 2069121−2069129 and 2069131−2069142 contain

the supplementary crystallographic data for this paper. These

data can be obtained free of charge via www.ccdc.cam.ac.uk/

data_request/cif, or by emailing data_request@ccdc.cam.ac.

uk, or by contacting The Cambridge Crystallographic Data

Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44

1223 336033.

{[Hg₂(μ₂-Br)₂(L6⁻)₂(L6)₂]} (9). A total of 0.23 mmol, 84 mg of

HgBr₂and 0.23 mmol of L6 (50 mg) were dissolved in a mixture of

methanol (6 mL) and THF (3 mL). The mixture was stirred for 4 h at

room temperature to yield to a turbid solution which was ﬁltrated,

yielding to a clear solution which was left for slow evaporation. Plate

colorless crystals were ﬁltered oﬀ after 10 days, washed with methanol

(3 mL), and dried under a vacuum and transferred into brown bottles

to prevent light exposure. Yield: (46 mg) 17%. Anal. Calc. for 9·

44H₂O (Hg₂C₂₂H₁₂₀N₂₀O₅₂Br₂): C, 13.04; H, 5.47; N, 12.67%;

Found: C, 13.56; H 2.38; N 11.93%. IR (KBr, cm⁻¹): 3210, 3035,

2620, 1560, 1480, 1330, 1270, 730.

AUTHOR INFORMATION

■

Corresponding Author

Yann Garcia − Institute of Condensed Matter and

Nanosciences, Molecular Chemistry, Materials and Catalysis

(IMCN/MOST), Université Catholique de Louvain, 1348

Louvain-la-Neuve, Belgium; orcid.org/0000-0002-3105-

0735; Email: yann.garcia@uclouvain.be

{[Hg₂(μ₂-I)₂(L6⁻)₂(L6)₂]} (10). A total of 0.16 mmol of HgI₂(74

mg) and 0.23 mmol of L6 (50 mg) were placed in the main arm of a

Γ glass tube which was ﬁlled with methanol. While the main arm was

heated in an oil bath at 60 °C, colorless, block-shaped crystals

deposited on the cooler arm after 12 days. These were ﬁltered oﬀ,

washed with methanol (3 mL), and dried in air. Yield: (165 mg) 56%.

Anal. Calc. for 10·3H₂O (C₂₄H₃₈I₂Hg₂N₂₀O₁₁S₄): C, 18.41; H, 2.45;

N, 17.89%; Found: C, 18,00; H, 2.18; N, 17.48%. IR (KBr, cm⁻¹):

3200, 3060, 1550, 1420, 1380, 1680, 810.

Authors

Houria Benaissa − Institute of Condensed Matter and

Nanosciences, Molecular Chemistry, Materials and Catalysis

(IMCN/MOST), Université Catholique de Louvain, 1348

Louvain-la-Neuve, Belgium

{[(Hg)₂(μ3-L5′)I₃]}_∝(11). A total of 0.29 mmol of HgI₂(132 mg)

and 0.27 mmol of L5′ (50 mg) were placed in the main arm of a Γ

glass tube which was ﬁlled with methanol. While the main arm was

heated in an oil bath at 60 °C, colorless, block-shaped crystals

deposited on the cooler arm after 13 days. These were ﬁltered oﬀ,

washed with a methanol (3 mL), and dried in air. Yield: (82 mg) 32%.

Anal. Calc. for 11 C₆H₈I₃Hg₂N₅S₄: C, 7.34; H, 1.03; N, 7.13%;

Found: C, 7.28; H, 1.18; N, 7.09%. IR (KBr, cm⁻¹): 3100, 2650,

1620, 1420, 1370, 1210, 1170, 1010, 640.

Nayarassery N. Adarsh − School of Chemical Sciences,

Mahatma Gandhi University, Kottayam 686560, Kerala,

India; orcid.org/0000-0003-2262-8512

Koen Robeyns − Institute of Condensed Matter and

Nanosciences, Molecular Chemistry, Materials and Catalysis

(IMCN/MOST), Université Catholique de Louvain, 1348

Louvain-la-Neuve, Belgium

Jakub J. Zakrzewski − Inorganic Molecular Materials Group,

Faculty of Chemistry, Jagiellonian University, 30-387

Krakow, Poland

Single Crystal X-ray Diﬀraction. Single crystal X-ray data of all

compounds were collected at room temperature with a MAR345

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Article

Transamination: An Avenue to an Auspicious Class of Supra-

molecular Synthons. Cryst. Growth Des. 2011, 11, 4034−4043.

(10) Naik, A. D.; Dîrtu, M. M.; Railliet, A. P.; Marchand-Brynaert, J.;

Garcia, Y. Coordination polymers and metal organic frameworks

derived from 1,2,4-triazole amino acid linkers. Polymers 2011, 3,

1750−1775.

(11) Kobalz, K.; Kobalz, M.; Möllmer, J.; Junghans, U.; Lange, M.;

Bergmann, J.; Dietrich, S.; Wecks, M.; Gläser, R.; Krautscheid, H.

Paddle Wheel Based Triazolyl Isophthalate MOFs: Impact of Linker

Modification on Crystal Structure and Gas Sorption Properties. Inorg.

Chem. 2016, 55, 6938−6948.

(12) Dong, Y.; Peng, P.; Hu, B.; Su, H.; Li, S.; Pang, S. High-Density

Energetic Metal −Organic Frameworks Based on the 5,5 ′-Dinitro-

2H,2 ′H-3,3 ′-bi-1,2,4-triazole. Molecules 2017, 22, 1068.

(13) Liu, B.; Yang, T. Y.; Feng, H. J.; Zhang, Z. H.; Xu, L. A 3D

chiral metal-organic framework based on left-handed helices

containing 3-amino-1 H-1,2,4-triazole ligand. J. Solid State Chem.

2015, 230, 90−94.

Szymon Chorazy − Inorganic Molecular Materials Group,

Faculty of Chemistry, Jagiellonian University, 30-387

Krakow, Poland; orcid.org/0000-0002-1669-9835

James G. M. Hooper − Department of Theoretical Chemistry,

Faculty of Chemistry, Jagiellonian University, 30-060

Krakow, Poland; orcid.org/0000-0003-3859-6172

Filip Sagan − Department of Theoretical Chemistry, Faculty of

Chemistry, Jagiellonian University, 30-060 Krakow, Poland;

orcid.org/0000-0001-5375-8868

Mariusz P. Mitoraj − Department of Theoretical Chemistry,

Faculty of Chemistry, Jagiellonian University, 30-060

Krakow, Poland; orcid.org/0000-0001-5359-9107

Mariusz Wolﬀ − Institute of Condensed Matter and

Nanosciences, Molecular Chemistry, Materials and Catalysis

(IMCN/MOST), Université Catholique de Louvain, 1348

Louvain-la-Neuve, Belgium; Institute of Inorganic Chemistry,

Johannes Kepler University Linz, 4040 Linz, Austria;

orcid.org/0000-0002-9265-7557

(14) Kitagawa, S.; Kitaura, R.; Noro, S. I. Angew. Functional Porous

Coordination. Angew. Chem., Int. Ed. 2004, 43, 2334−2375.

(15) Adarsh, N. N.; Novio, F.; Ruiz-Molina, D. Coordination

polymers built from 1,4-bis(imidazol-1-ylmethyl)benzene: from

crystalline to amorphous. Dalton Trans. 2016, 45, 11233−11255.

(16) Li, B.; Wen, H. M.; Zhou, W.; Chen, B. Porous Metal −Organic

Frameworks for Gas Storage and Separation: What, How, and Why? J.

Phys. Chem. Lett. 2014, 5, 3468−3479.

Smaail Radi − LCAE, Department of Chemistry, Faculty of

Sciences, University Mohamed I, 60 000 Oujda, Morocco;

orcid.org/0000-0002-5062-6904

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.cgd.1c00352

(17) Li, H.; Wang, K.; Sun, Y.; Lollar, C. T.; Li, J.; Zhou, H. C.

Recent advances in gas storage and separation using metal −organic

frameworks. Mater. Today 2018, 21, 108−121.

Notes

The authors declare no competing ﬁnancial interest.

(18) Li, J.-R.; Sculley, J.; Zhou, H.-C. Metal −Organic Frameworks

for Separations. Chem. Rev. 2012, 112, 869−932.

ACKNOWLEDGMENTS

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We acknowledge ﬁnancial support from FNRS (CDR

33694457, PDR T.0095.21), Wallonie Bruxelles International

(WBI COP22 Morocco, stipendium of excellence for H.B.),

CNRST (ESRFC-CNRST-P10) as well as FNRS-PAN and

WBI-MNiSW.

(19) Yu, X.; Wang, L.; Cohen, S. M. Photocatalytic metal −organic

frameworks for organic transformations. CrystEngComm 2017, 19,

4126−4136.

(20) Paul, M.; Adarsh, N. N.; Dastidar, P. Secondary Building Unit

(SBU) Controlled Formation of a Catalytically Active Metal −Organic

Polyhedron (MOP) Derived from a Flexible Tripodal Ligand. Cryst.

Growth Des. 2014, 14, 1331−1337.

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Exploring triazole-Thiourea Based Ligands for the Self-Assembly of Photoluminescent Hg(II) Coordination Compounds

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