Salicylaldehyde-(2-hydroxyethyl)imine - A flexible ligand for group 13 and 14 elements

Article abstract of DOI:10.1016/j.ica.2014.08.026

The reaction of salicylaldehyde-(2-hydroxyethyl)imine (H₂L), 1, with organoelement halides from group 13 and 14 leads to a variety of coordination compounds. Depending on the size of the central atom and the organic substituents, tetra-, penta- or hexacoordinated complexes emerge. When the central atom of the complex has a small atom radius and small substituents, like methyl groups, coordination number four is preferred. Thereby macrocyclic compounds of the composition L₂(SiMeR)₂ (R = Me, cyclohexyl) are formed. With phenyl substituted element halides Ph₂ECl₂ pentacoordinated complexes LEPh₂ (E = Si, Ge, Sn) were isolated. Hexacoordinated complexes of the composition L₂E (E = Si, Sn) were obtained from ECl4 and 1. A surprising result was obtained from the reaction of 1 with InCl₃. The resulting complex is a monoanionic trimer, obeying the composition [HNEt₃][L₃In₃Cl₃(μ₃-OH)].(DME)₂(THF) in the solid state structure. The prepared compounds were characterised by NMR and IR spectroscopy, elemental and X-ray structure analysis. Furthermore solid state NMR measurements and chemical shift tensor analysis with the help of quantum chemical methods were used to analyse the electron density distribution around the central atoms of several products. The results of this study demonstrate the structural variety that can be created with a single O,N,O' chelating ligand.

Full text of DOI:10.1016/j.ica.2014.08.026

Inorganica Chimica Acta 423 (2014) 268–280
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Salicylaldehyde-(2-hydroxyethyl)imine – A flexible ligand for group
13 and 14 elements
a
a
a
b
a,
⇑
Lydia E.H. Paul , Ines C. Foehn , Anke Schwarzer , Erica Brendler , Uwe Böhme
a
Institut für Anorganische Chemie, Technische Universität Bergakademie Freiberg, Leipziger Straße 29, D-09599 Freiberg, Sachsen, Germany
Institut für Analytische Chemie, Technische Universität Bergakademie Freiberg, Leipziger Straße 29, D-09599 Freiberg, Sachsen, Germany
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 May 2014
Received in revised form 5 August 2014
Accepted 7 August 2014
Available online 1 September 2014
The reaction of salicylaldehyde-(2-hydroxyethyl)imine (H L), 1, with organoelement halides from group
2
13 and 14 leads to a variety of coordination compounds. Depending on the size of the central atom and
the organic substituents, tetra-, penta- or hexacoordinated complexes emerge. When the central atom of
the complex has a small atom radius and small substituents, like methyl groups, coordination number
four is preferred. Thereby macrocyclic compounds of the composition L
are formed. With phenyl substituted element halides Ph ECl pentacoordinated complexes LEPh
E = Si, Ge, Sn) were isolated. Hexacoordinated complexes of the composition L
2 2
(SiMeR) (R = Me, cyclohexyl)
2
2
2
Keywords:
Schiff base ligands
X-ray diffraction
Silicon
Germanium
Tin
(
2
E (E = Si, Sn) were
obtained from ECl
complex is a monoanionic trimer, obeying the composition [HNEt
solid state structure. The prepared compounds were characterised by NMR and IR spectroscopy,
elemental and X-ray structure analysis. Furthermore solid state NMR measurements and chemical shift
tensor analysis with the help of quantum chemical methods were used to analyse the electron density
distribution around the central atoms of several products. The results of this study demonstrate the
4
and 1. A surprising result was obtained from the reaction of 1 with InCl
3
. The resulting
2
(THF) in the
3
3
][L
3 3
In Cl
3
(
l
-OH)]ꢀ(DME)
Indium
0
structural variety that can be created with a single O,N,O chelating ligand.
Ó 2014 Elsevier B.V. All rights reserved.
1
. Introduction
Schiff bases in general are versatile ligands [1–3]. Salicylalde-
it was shown that they are potent antitumor reagents [9]. There-
fore the large number of recently published reports regarding Si/
0
Sn complexes with tridentate O,N,O -ligands is not surprising
1
0
hyde-(2-hydroxyethyl)imine (H
2
L) has shown to be
a
good
[13–20]. Most of known O,N,O -ligands show a imine [19,21],
coordination partner for various elements or metals. Numerous com-
plexes have been prepared and characterised, see for instance the zinc
complexes published by Dey et al. [4]. Salicylaldehyde-(2-hydroxy-
ethyl)imine is able to form stable complexes with transition metals
amine [20] or aza [16] moiety. In comparison only few publications
exist dealing with germanium [6,22], indium [23] and aluminium
[24] Schiff base complexes.
The focus of the presented work lies on the synthesis and char-
acterization of new complexes with group 13 and 14 elements as
central atom and salicylaldehyde-(2-hydroxyethyl)imine as possi-
ble chelating ligand. Feasible similarities and/or differences in
complex formation, coordination numbers and crystal structures
are investigated. In addition, solid state NMR spectra are recorded
from selected substances to determine the silicon and tin NMR
chemical shift tensors.
[
5] and with group 14 elements [6]. Within these complexes, the O
donor atoms can act as bridge between metal centres yielding either
polynuclear complexes [6] or complexes with different stoichiometry
for the same metal [1].
Silicon and tin Schiff base complexes are a fast developing field
of research [7] which is due to their various possible applications.
These complexes can exhibit fungicidal [8,9], bactericidal [10],
antimicrobial [11] or bacteriostatic [12] properties. In some cases
2
. Experimental
⇑
Corresponding author. Tel.: +49 3731 392050; fax: +49 3731 394058.
E-mail address: Uwe.Boehme@chemie.tu-freiberg.de (U. Böhme).
The chemical name ‘‘salicylaldehyde-(2-hydroxyethyl)imin’’ is used throughout
2
.1. General considerations
1
All chemicals obtained from commercial suppliers were used as
this paper. It reflects the preparation and functionality of the ligand system in a
proper way. Alternative names would be: 2-(salicylidenamino)ethanol or (E)-2-{[(2-
hydroxyethyl)imino]methyl}phenol.
received. Since both the educts and the synthesized complexes are
sensitive to moisture, preparation was performed in Schlenk tubes
http://dx.doi.org/10.1016/j.ica.2014.08.026
0
020-1693/Ó 2014 Elsevier B.V. All rights reserved.

L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
269
under argon atmosphere using anhydrous and air-free solvents.
Melting points were determined with a Polytherm A from Wagner
vacuum before performing the elemental analysis. Thereby most
of the containing dichlorodimethylstannane was removed.
Otherwise the expected values for the complex found in the
1
13 119
&
Munz using samples in sealed capillaries. Standard H, C,
Sn,
2
9
and Si NMR solution spectra were recorded on a Bruker DPX 400
spectrometer at 293 K [ H (400.13 MHz), C (100.61 MHz), Si
X-ray structure would be the following: Anal. Calc. for the complex
1
13
29
.
(LSnMe
2
)
4
SnCl Me
2 2
with C46
H66Cl
N
2 4
O
8
Sn
5
(1467.49 g/mol): C,
1
19
Sn (149.17 MHz)]. 1H, 13C, Si chemical shifts
29
(
79.49 MHz),
37.65; H, 4.53; N, 3.82%.
1
19
119
are reported relative to tetramethylsilane,
Sn chemical shifts
Sn NMR (CDCl
3
): d ꢁ155.5 ppm (weak, broad).
Sn NMR (CPMAS): d ꢁ301 ppm.
H NMR (CDCl ): d 0.67, 1.61 (Sn–CH
ligand); 6.67–7.35 (m, 4H, CHar); 8.42 (s, 1H,
1
1
19
relative to tetramethyltin as external reference. Used solvents are
specified below.
3
3 2
); 3.70 (t, 2H, CH ligand);
The solid-state NMR spectra were recorded with a Bruker
4.09 (t, 2H, CH
2
2
9
Avance 400 WB spectrometer operating at 79.52 MHz ( Si) and
H–C@N) ppm.
1
19
29
13
1
49.24 MHz ( Sn), respectively. Si spectra were recorded by
C NMR (CDCl
3
): d 8.9, 15.3 (CH
3
); 60.0, 62.2 (CH
2
ligand);
116.2–167.0 (Ar); 171.6 (C@N) ppm.
2
IR: 2915 (CH O valence); 2826 (CH N valence); 1629 (C@N
CPMAS using a 7 mm probe, 5 ms contact time and a spinning
frequency of 4 kHz, if not noted otherwise. The chemical shift scale
m
2
4
was referenced with
109 ppm relative to TMS).
obtained using a 4 mm probe and single pulse excitation applying
0° pulses and repetition times of 30 s. The chemical shift was
referenced with SnO (-603 ppm relative to tetramethyltin) [25].
Q
8
M
8
(strongest shielded Q -group at
Sn solid state NMR spectra were
valence); 1621, 1449 (C@C valence phenyl); 494 (Sn–N valence);
119
ꢁ1
ꢁ
409, 403, 401 (Sn–O valence) cm
.
3: Dichlorodimethylsilane (2.35 g, 18.2 mmol) in THF (60 mL),
triethylamine (3.68 g, 36.4 mmol) and 1 (3.0 g, 18.2 mmol) in
THF (60 mL) yield yellow crystals (1.2 g, 30%), m.p. 371.6 K. Anal.
3
2
Principal components of the chemical shift tensor were calculated
from spinning side band spectra using DMFIT [26] and HBA [27].
IR spectra were recorded in the range 400–4000 cm at room
temperature with a Nicolet 380 FT-IR spectrometer. The samples
Calc. for C22
30 2 4 2
H N O Si (442.66 g/mol): C, 59.69; H, 6.83; N, 6.33.
Found: C, 59.75; H, 6.62; N, 6.60%.
ꢁ1
29
Si NMR (C
6
D
6
): d ꢁ8.9 ppm.
): d 0.07 (s, 6H, Si–CH
ligand); 6.60–7.09 (m, 4H, CHar); 8.33 (s, 1H,
1
H NMR (C
6
D
6
3 2
); 3.05 (m, 2H, CH ligand);
(
KBr pellets) were prepared under N
2
atmosphere. Elemental anal-
3.94 (s, 2H, CH
2
yses were performed with a Vario Micro CHNS.
H–C@N) ppm.
1
3
C NMR (C
117.2–161.7 (Ar); 166.4 (C@N) ppm.
IR: 1634 (C@N valence); 1115, 1050 (C-O fingerprint); 1582,
497(Car valence);1373(CH
4: Dichlorocyclohexylmethylsilane (3.59 g, 18.2 mmol) in
6
D
6
): d ꢁ3.1 (Si–CH
3 2
); 61.3, 61.5 (CH ligand);
2
.2. Synthesis of the ligand salicylaldehyde-(2-hydroxyethyl)imine (1)
[4]
m
ꢁ1
1
3
deformation);947(Si-Ostretch)cm .
2
-Amino-1-ethanol (6.11 g, 0.1 mol) was solved in methanol
50 mL) and slowly added to solution of salicylaldehyde
12.21 g, 0.1 mol) in methanol (100 mL). The resulting reaction
(
(
a
THF (60 mL), triethylamine (3.68 g, 36.4 mmol) and 1 (3.0 g,
18.2 mmol) in THF (60 mL) yield pale yellow crystals (1.8 g,
mixture was refluxed for 1.5 h. After cooling to room temperature,
the solvent was removed under reduced pressure. The raw product
was purified by fractioned distillation yielding an oily, orange-
yellow liquid. Yield: 12.3 g (74.5%); b.p. 156 °C at 0.6 kPa.
46 2 4 2
34.2%), m.p. 428.5 K. Anal. Calc. for C32H N O Si (578.89 g/mol):
C, 66.40; H, 8.01; N, 4.84. Found: C, 65.94; H, 7.41; N, 4.81%.
2
1
9
Si NMR (CDCl
H NMR (CDCl ): d 0.62 (t, 2H, CH
cyclohexyl); 0.17 (s, 3H, CH
ligand); 3.91 (m, 2H, CH ligand); 6.86–7.26 (m, 4H,
CHar); 8.32 (s, 1H, H–C@N) ppm.
3
): d ꢁ14.3 ppm.
3
2
cyclohexyl), 1.14 (m, 4H, CH
); 3.70
2
1
3
H NMR (CDCl
3
): d 3.65 (t, 2H, CH
2
,
J
HH = 5.0 Hz); 3.83 (t, 2H,
cyclohexyl), 1.66 (m, 4H, CH
(m, 2H, CH
2
3
3
CH
2
, JHH = 5.0 Hz); 6.81–7.29 (m, 4H, CHar); 8.27 (s, 1H, H–C@N).
2
2
1
3
C NMR (CDCl
32.7, 161.9 (CHar); 166.8 (C@N).
IR: 3363 (OH-valence); 1279 (OH fingerprint); 1151, 1067
C–O valence); 1633 (C@N valence); 1582, 1528 (Car valence);
3 2
): d 61.3, 61.9 (CH ); 117.3, 118.5, 118.6, 131.6,
1
3
1
C NMR (CDCl
61.7, 61.9 (CH ligand); 117.3–161.6 (Ar); 166.8 (C@N) ppm.
IR: 1644 (C@N valence); 1129, 1106 (C–O fingerprint); 1598,
1578 (Car valence); 1370 (CH deformation); 921 (Si–O stretch)
3 3 2
): d ꢁ4.4 (Si–CH ); 26.5–27.9 (CH cyclohexyl);
m
2
(
m
ꢁ1
7
58 (C–H deformation) cm
.
3
ꢁ
1
cm
.
2
.3. General procedure for the synthesis of the coordination
5: Reaction of dichlorosilacyclobutane (2.57 g, 18.2 mmol) in
THF (40 mL), triethylamine (4.05 g, 40.0 mmol) and 1 (3.0 g,
8.2 mmol) in THF (80 mL) was carried out as described above.
The raw material was solved in a DME-n-hexane mixture (1:1)
and filtered through SiO . Addition of diethylether and DME gives
compounds 2–11
1
The appropriate dichlorodiorganylsilane, -germane or -stannane,
SnCl
4
or InCl
3
was dissolved in tetrahydrofuran and cooled down
2
with an ice bath to 273 K. Triethylamine was added slowly, after-
wards a solution of 1 in tetrahydrofuran was added dropwise at this
temperature. Warming up to room temperature and stirring for
several days at r.t. forms a white precipitate. This triethylamine
hydrochloride was collected via suction filtration, washed with
tetrahydrofuran three times (à 10 mL). The solvent was removed
completely under reduced pressure to give a yellow residue. The
raw material was solved in dimethoxyethane (DME) and stored at
a solid which was separated via suction filtration. After seven days
storing at 253.2 K intense yellow crystals (1.1 g, 25.9%) were col-
lected. The compound seems to be relatively unstable outside the
mother liquid even under argon atmosphere. M.p. 410–412 K. Anal.
Calc. for C12H15NO Si (233.34 g/mol): C, 61.77; H, 6.48; N, 6.00.
2
Found: C, 60.76; H, 6.38; N, 5.83%.
2
2
1
9
9
Si NMR (CDCl
Si NMR (CPMAS): d ꢁ84.8 ppm.
): d 1.29–1.61 (m, 6H, CH
ligand); 6.97–7.08 (m, 2H, CHar); 7.33–
7.46 (m, 2H, CHar); 8.22 (s, 1H, H–C@N) ppm.
3
): d ꢁ81.5 ppm.
2
76 K for crystallisation process. Collection of the solid via suction
H NMR (CDCl
3
2
silacyclobutane);
filtration and drying in vacuum yield a bulk material for further
analysis.
3.70–4.03 (m, 4H, CH
2
1
3
2:
Dichlorodimethylstannane (4.00 g, 18.2 mmol) in THF
60 mL), triethylamine (3.68 g, 36.4 mmol) and (3.0 g,
8.2 mmol) in THF (60 mL) yield intense yellow crystals (1.4 g,
4.7%), m.p. 432.9 K. Anal. Calc. for the complex (LSnMe with
Sn (623.872 g/mol): C, 42.36; H, 4.85; N, 4.49. Found:
C NMR (CDCl
silacyclobutane); 53.4 (CH
120.3, 121.6, 130.9, 134.9, 159.0 (Ar); 159.5 (C@N) ppm.
IR: 2934, 2874 (C–H valence); 1640 (C@N valence); 1134,
1067 (C–O fingerprint); 1614, 1578 (Car valence); 1339 (CH defor-
3
): d 13.3 (CH
2
–Si, silacyclobutane); 27.4 (CH
2
(
1
2
ligand); 60.1 (CH
2
ligand); 119.4,
1
2
C
2
)
2
m
22
H
30
N
2
O
4
2
3
ꢁ
1
C, 41.34; H, 4.83; N, 4.40%. The sample was dried carefully in
mation); 914 (Si–O stretch) cm .

2
70
L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
6
: Dichlorodiphenylsilane (4.61 g, 18.2 mmol) in THF (60 mL),
.68 g triethylamine (36.4 mmol) and 1 (3.0 g, 18.2 mmol) in THF
60 mL) yield yellow crystals (1.27 g, 20.2%), m.p. 475.5 K. Anal.
Calc. for C21 Si (345.46 g/mol): C, 73.01; H, 5.54; N, 4.05.
IR:
2 2
m 2880 (CH O valence); 2814 (CH N valence); 1637 (C@N
3
(
valence); 1632, 1447 (C@C valence phenyl); 460 (Sn–N valence);
436, 439 (Sn–O valence) cm .
11: Indiumtrichloride (1.95 g, 8.8 mmol) in THF (30 mL), trieth-
ylamine (1.78 g, 17.6 mmol) and 1 (1.46 g, 8.8 mmol) in THF
(30 mL) yield intense yellow crystals (0.8 g, 25.7%), m.p. 516.0 K.
ꢁ1
H19NO
2
Found: C, 72.73; H, 5.49; N, 4.16%.
2
1
9
Si NMR (CDCl
H NMR (CDCl
3
): d ꢁ94.4 ppm.
3
): d 3.39 (t, 2H, CH
2
ligand); 4.22 (t, 2H, CH
2
33 3 3 4 7
Anal. Calc. for C H44 Cl In N O (without THF and DME;
ligand); 6.69–8.30 (m, 14H, CHar); 8.85 (s, 1H, H–C@N) ppm.
1059.54 g/mol): C, 37.40; H, 4.19; N, 5.29. Found: C, 37.51; H,
1
3
C NMR (CDCl
66.7 (C@N) ppm.
IR: 1666 (C@N valence); 1071 (C–O fingerprint); 1605, 1566
ar valence); 915 (Si–O stretch) cm
Dichlorodiphenylgermane (5.42 g, 18.2 mmol) in THF
60 mL), triethylamine (3.68 g, 36.4 mmol) and (3.0 g,
8.2 mmol) in THF (60 mL) yield intense yellow crystals (1.5 g,
1.1%), m.p. 357.6 K. Anal. Calc. C21 19GeNO (389.96 g/mol): C,
4.68; H, 4.91; N, 3.59. Found: C, 64.01; H, 5.74; N, 3.83%.
3
): d 53.3, 59.9 (CH
2
ligand); 117.1–161.3 (Ar);
3.98; N, 4.97%.
1
1
H NMR (CDCl
triethylammonium); 4.25 (t, 6H, CH
ligand); 6.62–7.09 (m, 12H, CHar); 8.32 (s, 3H, H–C@N);
10.34 (s, 1H, triethylammonium); 3.39 (m, 12H, CH DME); 3.54
3
): d 1.30 (t, 9H, CH
3
triethylammonium); 3.04 (q,
m
6H, CH
CH
2
2
ligand); 4.51 (t, 6H,
ꢁ1
(
C
.
2
7
:
3
(
1
(m, 8H, CH
2
DME) ppm.
1
3
1
2
6
C NMR (CDCl
3
): no resonances due to insufficient solubility.
2
O valence); 2871 (CH N
H
2
IR:
m
3315 (OH valence); 2990 (CH
2
valence); 1641 (C@N valence); 1629, 1477 (C@C valence phenyl);
1
ꢁ1
H NMR (CDCl
3
): d 3.77 (t, 2H, CH
2
ligand); 3.93 (t, 2H, CH
2
419 (In-N valence); 406 (In-O valence) cm
.
ligand); 6.87–7.59 (m, 14H, CHar); 8.41 (s, 1H, H–C@N) ppm.
1
3
C NMR (CDCl
67.3 (C@N) ppm.
IR: 1649 (C@N valence); 1100 (C–O fingerprint); 1584, 1529
ar valence) cm
Dichlorodiphenylstannane (6.26 g, 18.2 mmol) in THF
60 mL), triethylamine (3.68 g, 36.4 mmol) and (3.0 g,
8.2 mmol) in THF (60 mL) yield intense yellow crystals (2.8 g,
5.2%), m.p. 482.5 K. Anal. Calc. for C21 Sn (436.06 g/mol):
3
): d 62.1, 62.5 (CH
2
ligand); 117.3–161.3 (Ar);
1
2.4. Crystal Structure analyses of the synthesized complexes
m
ꢁ1
(
(
C
.
Single crystals of the complexes suitable for X-ray structure
analysis were grown from DME solution at 276 K and mounted
on a glass fiber and transferred to the nitrogen gas stream of the
8
:
1
1
3
diffractometer (BRUKER Kappa CCD X8 Apex II; Mo K
k = 0.71073 Å). The structures were solved by direct methods
SHELXS-97) and refined by full-matrix least-squares methods on
F for all unique reflections (SHELXL-97) [28]. The hydrogen atoms
were refined with a riding model. Crystallographic data of com-
a radiation,
H19NO
2
C, 57.84; H, 4.39; N, 3.21. Found: C, 57.66; H, 4.16; N, 3.24%.
(
1
1
19
2
Sn NMR (CDCl
3
): d ꢁ329.8 ppm.
H NMR (CDCl ): d 3.76 (t, 2H, CH
3
2
ligand); 4.27 (t, 2H, CH
2
ligand); 6.68–8.43 (m, 14H, CHar); 8.49 (s, 1H, H–C@N) ppm.
pounds 2–11 are summarised in Table 1.
1
3
C NMR (CDCl
40.6 (Ar); 171.9 (C@N) ppm.
IR: 1630 (C@N valence); 1055 (C–O fingerprint); 1599, 1543
ar valence); 447 (Sn–O valence) cm
: Reaction of silicon tetrachloride (1.55 g, 9.1 mmol) in THF
30 mL), triethylamine (4.0 g, 39.3 mmol) and 1 (3.0 g, 18.2 mmol)
3
): d 59.8 (CH
2
ligand), 62.5 (CH
2
ligand); 116.4–
1
2.4.1. Quantum chemical calculations
m
ꢁ1
The DFT calculations were carried out using GAUSSIAN 09 [29].
NMR shielding tensors were calculated with the Gauge-Indepen-
(
C
.
9
2
9
dent Atomic Orbital method (GIAO) [30]. Si NMR data were
calculated using the B3PW91 [31,32] density functionals, in
combination with the 6-311+G(2d,p) [33–35] basis set for all
atoms, with the geometries from X-ray structure analyses.
Calculated absolute shielding values were converted to relative
shifts d with the calculated shielding for tetramethylsilane at the
same level of theory.
(
in THF (70 mL) was carried out as described above. In addition to
stirring at room temperature, the reaction mixture was stirred
overnight at this temperature, refluxed for 7 h and afterwards at
r.t. for four days. The raw material was solved in a DME-n-hexane
mixture (1:1), filtered and washed with diethylether to give a yel-
low crystalline solid (0.99 g, 30.7%), m.p. 498–501 K (decomposi-
119Sn NMR data were calculated using the B3PW91 density
functionals, in combination with the DGDZVP [36] basis set for
tin and the 6-311+G(2d,p) basis set for all other atoms, with the
geometry from X-ray structure analysis. The calculated absolute
shielding value for compound 8 was converted to relative shift d
by setting the calculated isotropic shift equal to the measured
value. This leads to smaller differences than using the calculated
shift of tetramethyltin.
18 2 4
tion starting at 473 K). Anal. Calc. for C18H N O Si (354.44 g/
mol): C, 61.00; H, 5.12; N, 7.90. Found: C, 60.87; H, 5.09; N, 7.97%.
2
2
1
9
9
Si NMR (CDCl
Si NMR (CPMAS): d ꢁ172.22, ꢁ172.58 ppm.
): d 3.84–4.08 (m, 8H, CH ligand); 6.70–6.74 (m,
3
) d ꢁ172.46 ppm.
H NMR (CDCl
3
2
4
H, CHar); 7.21–7.32 (m, 4H, CHar); 8.28 (s, 2H, H–C@N) ppm.
1
3
C NMR (CDCl
17.5, 121.1, 132.6, 136.1, 162.7 (Ar); 164.6 (C@N) ppm.
IR: 2937. 2866 (C–H valence); 1631 (C@N valence); 1088 (C-O
fingerprint); 1609, 1533 (Car valence), 755 (Si–O valence) cm
0: Tintetrachloride (1.18 g, 4.5 mmol) in THF (60 mL), triethyl-
3 2 2
): d 56.1 (CH ligand); 58.6 (CH ligand); 117.1,
1
m
ꢁ1
.
1
3. Results and discussion
amine (3.68 g, 36.4 mmol) and 1 (1.5 g, 9.1 mmol) in THF (30 mL)
yield intense yellow crystals (0.9 g, 44.9%), m.p. 526.0 K. Anal. Calc.
The reaction of dichlorodiorganosilanes, -germanes and
stannanes with ligand 1 should lead to the formation of mononu-
-
for C18
H
18
2
N O
4
Sn (445.04 g/mol): C, 48.58; H, 4.08; N, 6.29. Found:
C, 49.83; H, 4.47; N, 6.22%.
clear pentacoordinated complexes with one ligand molecule per
1
1
19
Sn NMR (CDCl
3
): d ꢁ573.27 ppm.
central atom Si, Ge, and Sn. In contrast, ECl
is expected to give mononuclear hexacoordinated complexes of
the EL type bearing two ligand molecules. The isolated products
4
as starting material
H NMR (CDCl ): d 3.83 (m, 4H, CH ); 4.10 (t, 4H, CH ); 6.72–
3
2 2
7
.32 (m, 8H, CHar); 8.48 (s, 2H, HC@N); impurities: 1.43, 3.39 (tri-
2
ethylamine hydrochloride); 1.66, 3.68 (THF); 3.54, 3.64 (DME)
ppm.
were characterised with NMR and IR spectroscopic methods.
Single crystal X-ray structure determination was used to eluci-
date the molecular structures and the coordination geometries
of the central atoms.
13C NMR (CDCl
3
2
): d 57.4, 60.7 (CH ligand); 117.3–167.8 (Ar);
1
71.8 (C@N); solvents: 58.9, 69.1 (DME); 25.3, 71.8 (THF) ppm.

L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
271
2 2
3.1. Reaction of ligand 1 with compounds R ECl
3.1.1. Synthesis and structure description of alkylated group 14
derivatives
Alkyl and aryl disubstituted dichlorostannanes, -silanes, and
germanes were used to form mononuclear pentacoordinated
complexes (Fig. 1).
The solution of the reaction mixture of 2 shows a weak broad
resonance at -155.5 ppm. This is in between the chemical shift
range of 4- and 5-fold coordination for this class of substances
and may indicate a fast change of the coordination geometry within
1
19
the solution. The
Sn solid state NMR spectrum of the amorphous
product 2 showed the expected fivefold coordinated complex hav-
1
99
ing a d( Sn) = ꢁ301 ppm. Attempts were undertaken to grow
crystals suitable for X-ray diffraction, but did not succed from CHCl
3
as solvent. At least single crystals of 2 were isolated from DME
solution. Surprisingly, the X-ray structure shows a different
coordination mode of the Sn atoms than the solution and solid state
NMR data. Indeed, Sn atoms appear as penta- and hexacoordinated
complex with a ratio of the tin atoms of 2:2:1 (for Sn1:Sn2:Sn3).
Sn2 shows a pentacoordinated environment while Sn1 and Sn3
are hexacoordinated. It is assumed that these associates found in
the crystal structure dissociate in solution (see Fig. 1).
Complex 2 was found to crystallise in the triclinic space group
P1 with two independent half molecules in the asymmetric unit.
ꢀ
2
-I represents a dimer created by an inversion centre in the centre
[
i]
[i]
of the four-membered ring, Sn1–O1–Sn1 –O1 (Symmetry code:
i] 1 ꢁ x, ꢁy, 1 ꢁ z). Sn1 is surrounded by three oxygen atoms,
[
one nitrogen and two carbon atoms resulting in a hexacoordinated
environment. The bond angles at Sn1 indicate a distorted octahe-
dral coordination sphere. The Sn–O-bond lengths show a slightly
longer phenolic O–Sn (Sn1–O2: 2.2178 Å) bond than an alcoholic
O–Sn bond (Sn1–O1: 2.1141 Å). This is caused by the conjugation
of the shorter C5–O2 (1.305 Å) with the aromatic moiety leading
to a longer O2–Sn1 bond. The longer aliphatic C1–O1 bond
(
1.406 Å) results in a shorter O1–Sn1 bond.
The second molecule, 2-II, of the obtained crystal structure pos-
sesses two different tin atoms with Sn3 situated on an inversion
centre. This Sn3 atom comes from the starting material, Me SnCl
2
2
,
to which two molecules of the expected pentacoordinated complex
are bound via the oxygen atom O3 (Fig. 1).
As observed with 2-I, the Sn–O bonds are of different length
depending on the adjacent C–O bond. The longest and therefore
weakest bond in the molecule is the bridging Sn3–O3 bond with
2
.244 Å. The octahedral coordination environment of Sn3 is repre-
sented in the angles at Sn3. This is in contrast to the NMR data. But
dissociation of the molecule in solution leads to the formation of
two equivalents of pentacoordinated complex and one equivalent
2 2
of the tetracoordinated educt molecule, Me SnCl , which is in
agreement with the spectral data. The last tin atom, Sn2, shows a
pentacoordinated environment. The coordination geometry in pen-
tacoordinate complexes can best be described with the parameter
s
which is defined as
second largest angle at the central atom. If
pyramid is described, while = 1 indicates a perfect trigonal bipyr-
amid [37]. In the case of Sn2 in 2-II, the geometry parameter
= 0.36 indicates a distorted square pyramidal geometry.
[39] interactions (see
s
= (b ꢁ
a
)/60° with b as largest and
a as the
s
= 0 a perfect square
s
s
Though different C–Hꢀ ꢀ ꢀO [38], C–Hꢀ ꢀ ꢀ
p
Supplementary material, Table S1) of moderate strength are pres-
ent in the crystal structure, these intermolecular contacts show
no significant influence on the molecular geometry. The phenyl
moieties are involved in C–Hꢀ ꢀ ꢀ
while stacking interactions are absent.
Using Me SiCl instead of Me SnCl leads to the formation of
yellow crystals of 3. The vibrational spectrum proves the absence
p contacts in the range of 3.5 Å,
p–p
2
2
2
2

2
72
L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
Fig. 1. Reaction of ligand 1 with Me
2
SnCl
2
and the identified products in solution and the solid state including the molecular structure of compound 2 and the used atomic
numbering scheme. The thermal ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level. Hydrogen atoms and the disorder at C10 in two positions are
omitted for clarity.
ꢁ
13
1
of a hydroxyl group. The signals at 947 cm indicate the presence
of a Si–O bond. In contrast, the 1H and C NMR data show no
significant changes in comparison to the isolated ligand 1. The
relevant C–Hꢀ ꢀ ꢀ
p
[39] or C–Hꢀ ꢀ ꢀO/N interactions [38]. In contrast,
the packing of 3 reveals several different intermolecular interac-
tions. First, C–Hꢀ ꢀ ꢀO/N contacts in the range from 2.49 to 2.61 Å
for the hydrogen-acceptor distance and 3.20–3.53 Å for the
donor–acceptor distance (h = 126–170°) appear. In addition, C–
2
9
Si chemical shift in solution reveals the existence of a tetracoor-
dinated Si species with a signal at ꢁ8.9 ppm. Therefore, the forma-
tion of a mononuclear pentacoordinated complex is doubtful.
Similar results were found for the reaction with dichloro(cyclo-
hexyl)(methyl)silane forming 4: (1) a disappearing hydroxyl group,
Hꢀ ꢀ ꢀ
p contacts are in the range of 2.70–2.85 Å (144–172°) as a part
of the network of significant intermolecular interactions generat-
ing the molecular packing.
ꢁ1
(
a
2) a Si–O stretch vibration at 921 cm in the IR spectrum, and (3)
2 2 6 2
While neither Me SiCl nor Me(C H11)SiCl react with 1 to give
mononuclear pentacoordinated complexes we decided to test
dichlorosilacyclobutane as starting material (Fig. 3).
2
9
Si chemical shift at ꢁ14.3 ppm indicating a tetracoordinated Si
compound.
Single crystals of both compounds 3 and 4 were grown from DME
The intense yellow compound 5 gives a 29Si NMR signal at
ꢁ81.5 ppm in chloroform solution and ꢁ84.8 ppm in the solid
state. This indicates the same geometric environment at the silicon
atom in solution and the solid state as well as a pentacoordinated
central atom. Single crystals were obtained from DME solution and
the expected coordination at the silicon atom was proven with
X-ray structure analysis.
solutions. Fig. 2 shows the molecular structures of 3 and 4. Bothcom-
plexes crystallise in the triclinic space group P1, 3 with two half mol-
ꢀ
ecules, and 4 with half a molecule in the asymmetric part of the unit
cell connected via an inversion centre. Both, 3 and 4, are 18-mem-
bered macrocyclic compounds (Scheme 1, Fig. 2). The formation of
a macrocycle consisting of two diorganosilicon moieties and two
ligand molecules leads to the preferred tetracoordinated environ-
ment of the silicon atoms as indicated in the spectroscopic analyses.
The two independent molecules of 3 differ significantly in the
Si–O bond lengths and C/O–Si–C/O angles to one another and
within one molecule. The geometric parameters of the central Si
atoms indicate a slightly distorted tetrahedral coordination sphere.
The C/O–Si–O angles lie between 106.1 and 113.1° (average:
In detail, 5 was found to crystallise with one independent mol-
ecule in the asymmetric part of the unit cell in the monoclinic
space group C2/c. Selected geometric parameters are given in
Table 2 and reveal a distorted trigonal bipyramidal coordination
of the silicon atom. The equatorial positions in this coordination
polyhedron are occupied by the atoms O1, O2, and C12. N1 and
C10 are at the apical positions with an bond angle N1–Si1–
C10 173.10(8)°. All bond lengths and angles including those
involving silicon are in the range of the expected values for such
coordination geometry. Moreover, the conjugated plane of the
1
09.5°) in 3-I and between 105.5° and 114.6° (average: 109.5°) in
-II. The plane generated by the macrocycle is not planar due to
3
2
3
the sp and sp hybridisation of the atoms involved. In both mole-
cules, the phenyl rings are orientated outside the macrocycles.
A similar geometric situation is found in the crystal structure of
possessing a slightly distorted tetrahedral coordination environ-
ment as well. The C/O–Si–C/O bond angles range from 105.3° to
13.5° (average: 109.5°). Once again, the Si–O bond lengths differ
ligand,
6 4
C H (O)C@N, is planar with a r.m.s. deviation of
0.0244 Å. The silicon atom is not situated in this plane but shows
a distance to the plane of 0.4946 Å.
Intra- or intermolecular interactions of 5 does not influence the
molecular structure but the molecular packing within the crystal
4
1
significantly but are still in the range of the expected value of a
Si–O single bond. As specified by the torsion angles and the hybrid-
isation of the involved atoms, the macrocycle is not planar. Again,
the phenyl rings are orientated outside the macrocycle.
Though the molecular structures of 3 and 4 are very similar,
their crystal packing are not. Hence, 4 is only subjected to
closed-packing and maximum symmetry effects and shows no
structure. The aryl ring interacts in a
centre-to-centre distance of 3.9846(11) Å and
1.957 Å. Additionally, the silabutane moiety interacts with the aryl
type of interaction (2.89 Å, h = 139°). As expected,
the oxygen atoms are able to take part in C–Hꢀ ꢀ ꢀO interactions
forming several intermolecular contacts (see Supplementary
material, Table S2).
p
–
p
stacking contact with a
a
slippage of
ring in a C–Hꢀ ꢀ ꢀ
p

L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
273
Fig. 2. Molecular structure of the crystallographic independent molecules I and II of 3 and 4 showing the atomic numbering scheme. The thermal ellipsoids of the non-
hydrogen atoms are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.
Table 2
Selected geometric parameters (Å, deg) in compound 5.
R2
Si
OH
N
O
O
R1
5
N
+
4 NEt
3
Si1–O1
Si1–O2
Si1–C12
Si1–C10
Si1–N1
s
1.6868(14)
1.7096(14)
1.892(2)
1.910(2)
1.9871(17)
0.79
2
2 2
+ 2 R SiCl
O
OH
- 4 HNEt Cl
3
R2 Si
R1
O
N
1
a
Siꢀ ꢀ ꢀA in Å
0.4946
1
= R2 = Me
2
a
3
:
4
:
R
R
A is defined as the least-square plane of the fol-
1
= Me; R = cyc-Hexyl
lowing atoms C3–C9, O2, N1.
2 2 6 2
Scheme 1. Reaction of ligand 1 with Me SiCl and Me(C H11)SiCl .
3.1.2. Synthesis and comparative reflections on the crystal structures
of the monomeric arylated group 14 derivatives
Only the inflexible silacyclobutane derivative was able to give
2 2
mononuclear pentacoordinated complexes of the type L ER .
Hence, the overall results of the reaction between ligand 1 and
alkylated group 14 derivatives are as follows. The cyclic derivative
5
(
shows the expected pentacoordinated Si complex. Me
2 2
ECl
Therefore, phenyl substituted derivatives were applied to check
the influence of the aromatic character of the substituents on the
molecular geometry of the complex formation (Scheme 2).
First, the vibrational IR spectra of all three compounds 6–8 give
no hint of the existence of a hydroxyl group present in the isolated
E = Si, Sn) give either the macrocylic tetracoordinated silicon
compound (3) or a mixture of penta- and hexacoordinated tin com-
plexes (2) in the solid state. Compound 2 shows different coordina-
tion modes. The tin atoms are tetra- and pentacoordinated in
chloroform solution. Penta- and hexacoordinated species were
proved to exist in the solid state structure. These species dissociate
in solution.
ꢁ
1
ꢁ1
product. Stretch vibrations at 915 cm (6) and 447 cm (8) indi-
1
3
cate the Si–O and Sn–O bond formation. Solution C NMR data of
complexes 6–8 show a slight change in the chemical shift of both
2
the imine and the CH moiety of ligand 1 giving a second hint for
successful coordination at the central atom. The chemical shifts
2
9
119
in the Si NMR spectrum of 6 at d ꢁ94.4 ppm and in the
Sn
NMR spectrum of 8 at d ꢁ329.8 ppm imply the formation of higher
coordinated species in both cases.
Though the crystal structure of 8 has been described previously
[
40], we decided to remeasure the obtained crystal to ensure the
results of the presented synthetic pathway. Indeed, the pentacoor-
dinated environment of the central Sn atom was confirmed. In the
following our data set is used for reflective comparisons of the
crystal structure of 6–8. Single crystals of 6–8 suitable for X-ray
structure analysis were yielded by slow crystallisation from DME
solution under inert conditions. While Fig. 4 illustrates the molec-
ular structure of the products, Table 3 presents relevant geometric
parameters.
The complexes of Ge and Sn, 7 and 8, crystallise in the same tri-
clinic space group, P1 with one molecule in the asymmetric part of
2 3 2
Fig. 3. Reaction of ligand 1 with dichlorosilacyclobutane, (CH ) SiCl . The molec-
ular structure of 5 shows the atomic numbering scheme. The thermal ellipsoids of
ꢀ
the non-hydrogen atoms are drawn at the 50% probability level.
the unit cell with similar unit cell dimensions and atom positions.

2
74
L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
expected. The ratios of the element-nitrogen bonds feature other
OH
O
E
N
N
Ph
Ph
deviations. While the Ge–N is slightly shorter than expected, the
Sn–N bond is substantial shorter indicating a stronger coordinative
bond between Sn and N than between Si/Ge and N. Nevertheless,
the differences are rather small. Moreover, all bond lengths and
angles apart from the central atom are in the range of the expected
values.
+
2 NEt
3
+
2 2
Ph ECl
OH
- 2 HNEt
3
Cl
O
1
6: E = Si
7
8
:
:
E = Ge
E = Sn
Comparison of the geometric parameters leads to no general
trend regarding the pentacoordinated environment of the central
2 2
Scheme 2. Reaction of ligand 1 with dichlorodiphenyl derivatives, Ph ECl .
atom. In case of 6
s
1
= 0.59 and
s
2
= 0.59, for complex 7
s = 0.68,
and complex 8 features a value of
s
= 0.55. All values indicate
strong distortion at the central atom with a slight tendency
towards trigonal bipyramidal coordination.
Therefore, 7 and 8 are said to be isomorphous. The molecular
overlay is depicted in Fig. 5(d) and will be discussed later on. In
contrast, 6 is not isomorphic to 7 and 8 since it crystallises in the
monoclinic space group P2 /n with two independent molecules
1
in the asymmetric unit.
The molecular structures of 6–8 represent each a pentacoordi-
nated compound with one ligand molecule coordinated at central
group 14 elements Si, Sn or Ge, respectively. The ratio of atom radii
of silicon (1.173 Å), germanium (1.223 Å) and tin (1.399 Å) [41] is
given with: 1:1.04:1.20. The bond ratios derived from the X-ray
structures are shown in Table 4. For the Ge–O bond, the ratio is
slightly higher than calculated indicating a weaker Ge–O bond
compared to the Si–O bond. In contrast, the Sn–O appears as
As mentioned above, 7 and 8 are isomorphous crystal struc-
tures. Hence, as indicated in Fig. 5(d), the molecular geometries
are very similar. Apart from the central atom, the ligand itself
has an influence on the molecular structure of the whole complex.
The conjugated part of the ligand, C H (O)C@N, is planar in all
6
4
three structures, 6–8, with r.m.s. deviations of 0.03–0.05 Å.
Besides, the aliphatic moiety, –CH –CH O–, is more flexible and
2
2
adjusts to the requirements of the central atom. This is illustrated
by the angles at the central atom and the distance of the central
atom to the least-squares plane of the conjugated moiety of the
ligand (C3–C9, O2, N1, Table 3). Indeed, the latter shows no real
trend for the group 14 elements.
Fig. 4. Molecular structure of the crystallographic independent molecules 6-I, 6-II, 7, and 8 showing the atomic numbering scheme. The thermal ellipsoids of the non-
hydrogen atoms are drawn at the 50% probability level.

L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
275
Table 3
Selected geometric parameters (Å, deg) in compounds 6–8, standard deviations are omitted for clarity.
d
E1–O1
E1–O2
E1–C10
E1–C16
E1–N1
s
Eꢀ ꢀ ꢀA in Å
6
6
-I
-II
7
1.672
1.673
1.871
2.046
1.707
1.713
1.970
2.108
1.917
1.916
1.957
2.131
1.880
1.878
1.959
2.119
2.046
2.042
2.015
2.187
0.59
0.59
0.68
0.55
0.460
0.324
0.687
0.447
a
8
b,c
Bond ratio
1:1.12:1.22
1:1.14:1.23
1:1.00:1.11
1:1.04:1.13
1:0.99:1.07
a
b
c
N1 = N2; C10 = C31; C16 = C37; O2 = O4; O1 = O3.
Atom radii of Si (1.173 Å), Ge (1.223 Å), Sn (1.399 Å) [41]; resulting ratios: Si:Ge:Sn:1:1.04:1.20.
Due to the similarity of 6-I and 6-II, only 6-I is used representing the Si derivative.
d
A is defined as the least-squares plane of the following atoms C3–C9, O2, N1; C24–C30, O4, N2.
Fig. 5. Least-squares overlays of (a) 6-I and 6-II, b) 6-I and 7, c) 6-I and 8, and d) 7 and 8. The r.m.s. deviations are (a) 0.0304 Å, (b) 0.0404 Å, (c) 0.050 Å, and (d) 0.0353 Å for an
overlay of the following atoms: O2/O4, N1/N3, C3–C9/C24–C30. All hydrogen atoms are omitted for clarity.
To sum up, the differences in the molecular structure cannot
only be explained by the size of the central atom and its fit in
the ‘‘bite’’ of the ligand. Moreover, the flexibility of the 2-oxyethyl
moiety of the ligand has a significant influence on the geometry of
the whole complex. Other influences are packing effects, inter-, and
intramolecular interactions. Especially the intramolecular C–Hꢀ ꢀ ꢀO
contacts of the phenyl ring (see Supplementary material, Table S3)
reveal a significant effect.
In silicon complex 6 only one out of two phenyl rings present in
the structure participates in intramolecular C–Hꢀ ꢀ ꢀO interactions
using the ortho substituted hydrogen atoms. As a result this phenyl
ring (C16–C21) is not co-planar to the plane of the ligand as the
other one (C11–C15) is. Similar contacts are found in the structures
of 7 (Ge) and 8 (Sn). But there, both phenyl rings are involved.
Therefore, both phenyl rings leave the plane of the ligand. Apart
from the intramolecular interactions mentioned above, several
other contacts of the type C–Hꢀ ꢀ ꢀO and C–Hꢀ ꢀ ꢀ occur in the crystal
p
packing. Stacking interactions of the aromatic units are not present.
The superimposed molecular structures depicted in Fig. 5 illus-
trate the differences of the molecular geometry depending on the
central atom. The deviation between both crystallographic inde-
pendent molecules of 6 should be caused by packing effects and
illustrate the flexibility of the ligand system (Fig. 5a). The superim-
posed structures of the silicon complex 6-I with the germanium
and tin complexes (Fig. 5b and c) reveal large differences in the
bond angles N–E–C and C–E–C. This leads to different orientations
of the phenyl groups. The best fit between two structures in this
series was found in the overlay of the germanium and the tin com-
plexes (Fig. 5d). This was expected, since both X-ray structures are
isomorphous.

2
76
L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
3.2. Synthesis and comparative reflections on the crystal structures of
Table 4
Selected geometric parameters (Å, deg) in compounds 9 and 10, standard deviations
are omitted for clarity.
group 14 derivatives with composition EL
2
E–Oa,b
E–Na,b
Eꢀ ꢀ ꢀA1 in Å
0.2154(9)
c
Eꢀ ꢀ ꢀA2 in Å
0.3225(9)
c
A1/A2 in deg
As mentioned above, the reaction of a diorganodichlorosilane, -
germane or –stannane with 1 leads to the formation of monomeric
pentacoordinated compounds 5–8 or to dimer or macrocyclic com-
9
10
1.756
2.024
1.893
2.154
84.83(3)
67.80(8)
0.3391(41)
0.7580(36)
plexes 2–4. Moreover, the reaction of ECl
meric hexacoordinated compounds with two ligands in the
4
with 1 results in mono-
a
Average values are given for the reason of clarity.
Single bond lengths: Si–O (1.91 Å), Si–N (1.91 Å), Sn–O (2.14 Å), Sn–N (2.14 Å)
b
coordination sphere of E (Scheme 3).
[41];
c
As expected for 10, the 119Sn NMR spectrum shows one peak at
A is defined as the least-squares plane of the following atoms: A1 (C3–C9, O2;
N1), A2 (C12–C18, O4, N2).
d ꢁ573.3 ppm, which implies that a hexacoordinated tin atom is
present at least in solution. The 1H and C NMR spectra support
the conclusion that a complex was formed since the resonances
13
The comparison of the E–N and E–O bond lengths of the penta-
coordinated complexes 6 and 8 to the hexacoordinated compounds
2
for both the CH groups and the imine group of the ligand are
shifted in comparison to the isolated ligand 1. The IR data of the
9
and 10 reveals remarkable effects. The bond lengths involving tin
become shorter by the change from penta- to hexacoordination
Sn–N: 2.19 ? 2.15 Å; Sn–O: 2.08 ? 2.02 Å). The Si–O bond gets
ꢁ1
obtained product show the appearance of Sn–N (460 cm ) and
ꢁ1
Sn–O (439 cm ) bonds while any hydroxy group is absent.
The growth of single crystals of 9 and 10 was successful from
DME solution. Similar to the monomeric derivatives 6 and 8, the
silicon and tin complexes 9 and 10 crystallise in different, not iso-
morphous space groups. Compound 9 was found to crystallise in
(
slightly longer (1.69 ? 1.76 Å), while the Si–N bond shortens
significantly (2.04 ? 1.89 Å).
The planar structure of the conjugated moiety of the ligand, C6-
4
H (O)C@N, was calculated as described above for compounds 6–8.
The calculated r.m.s. deviations in 9 and 10 are 0.01–0.04 Å. The
distances of the central atom to this plane are similar in 9, but
ꢀ
the monoclinic space group P1, 10 in the orthorhombic space
group Pca2
Fig. 6).
Both complexes show octahedral coordination geometry and
1
, each with one molecule in the asymmetric unit
(
1
0 shows an offset of about 0.4 Å indicating a non-central position
of the Sn atom (Table 4).
represent the meridional isomers. This leads to a situation where
all four oxygen atoms are situated in one plane while the nitrogen
atoms represent the tops of the octahedron. As indicated in Table 4,
the averaged Si–N bond length in 9 is in the range of the expected
values for a Si–N single bond (Si–N: 1.91 Å, [41]), while the Si–O
bond length is shortened (Si–O: 1.91 Å, [41]). A similar situation
is found in 10. While the averaged Sn–O bond length is shortened
Intramolecular interactions influencing the molecular geometry
significantly are not present in both crystal structures of 9 and 10.
On the other hand, the molecular packing differs significantly from
the Si to Sn compound. While 9 is dominated by several
ing (3.9 Å, slippage: 2.432 Å) and C–Hꢀ ꢀ ꢀ interactions in the range
of 2.68 Å (angle around H: 147°), 10 does not show any involved
p–p stack-
p
p
contacts. Both crystal structures reveal C–Hꢀ ꢀ ꢀO interactions of
moderate strength (see Supplementary material, Table S4). The
synthesis of 9 and 10 demonstrates the ability of ligand 1 to form
hexacoordinated complexes.
(
Sn–O: 2.14 Å, [41]), the Sn–N bond length is as expected (Sn–N:
2
.14 Å, [41]).
3.3. Synthesis and structure description of a group 13 derivative
OH
N
O
O
Salicylaldehyde-(2-hydroxyethyl)imine (1) was reacted with
N
O
N
+
4 NEt
3
InCl
3
in order to test the suitability of 1 as ligand towards group
+
ECl
4
E
OH
- 4 HNEt
3
Cl
1
1
3 elements. The H NMR spectrum of complex 11 indicates a com-
O
plex formation but due to the poor solubility of this complex no
further information could be gained from any NMR spectra deter-
mined in solution. However, the infrared spectrum of 11 shows the
1
9: E = Si
0: E = Sn
1
ꢁ1
OH valence vibration band is still present at 3315 cm . In addi-
tion, In-N and In-O valence vibration bands appear at 419 and
4
Scheme 3. Reaction of ligand 1 with ECl .
Fig. 6. Molecular structure of 9 and 10 showing the atomic numbering scheme. The thermal ellipsoids of the non-hydrogen atoms are drawn at the 50% probability level.
Solvent molecules are omitted for clarity in the case of compound 9.

L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
277
4
06 cmꢁ1. These results suggest either an incomplete reaction to a
tion. To describe the conformation of a six-membered ring the Cre-
mer Pople puckering parameters are applied [42,43]:
= 0.020(2) Å, q = 1.149(2) Å, = 128(6)°, # = 0.00(10)° and a
puckering amplitude of Q = 1.149(2) Å indicate the chair conforma-
tion. The average bond length within the ring is 2.157 Å. In con-
trast, the angles differ depending on the affected atom. While the
average angle around the oxygen atom is 107.3°, the In atoms show
complex mixed with free ligand 1 or a different coordination mode
of the ligand 1 with at least one hydroxyl group. Due to the shift of
the OH valence vibration from 3363 to 3315 cm the last possibil-
ity is more appropriate.
While the spectroscopic data does not reveal a definite struc-
ture of the achieved coordination compound, the X-ray diffraction
experiment with suitable single crystals grown from DME solu-
tions gives a surprising result. Complex 11 (Scheme 4) was found
&
q
2
3
u
2
ꢁ1
an average angle of 97.5°. Additionally, the three In atoms of the
3
six-membered ring are bridged with a
l
-OH group forming a tet-
ꢀ
to crystallise in the triclinic space group P1 with one indium con-
racyclic moiety. To the best of our knowledge, this conformation
was not observed so far for indium complexes. The reported struc-
ture of a polycyclic In-O-complex represents a distorted cube [44].
taining molecule in the asymmetric part of the unit cell. The ana-
lysed complex is neither neutral nor positive charged but
monoanionic with three indium atoms in the asymmetric unit
The structural motif featuring an [M–O]
is bridged by a l -OH group was found in several copper com-
3
six-membered ring which
3
(Fig. 7). A triethylammonium cation acts as counterion and is solv-
atized by one DME molecule. A second DME molecule is disordered
in two positions. Additionally, most likely a THF molecule is part of
the unit cell. It is not possible to localise or refine all atom positions
of the latter one. The overall composition of 11 in the solid state is
plexes with pentacoordinated central atoms [45].
In 11, the geometry at each In atom is best described as a dis-
torted octahedron with a coordination number of six. In addition
3
to the
l
-OH group, three chlorine and three ligand molecules
3
.
therefore [HNEt
][L In
3 3 3
Cl
3
(l
-OH)] (DME)
2
(THF) with L = 2-[(2-
are involved in the complex formation. Each of the alcoholic O
atoms (O1, O3, O5) of the ligand is shared by two In atoms. The
phenolic O atom, the N atom, and the Cl atoms are coordinated
to only one In atom each (Fig. 7).
oxidobenzylidene)amino]ethanolat.
The anion of 11 consists of an alternating In-O six-membered
ring (In1-O1-In2-O3-In3-O5) adopting the typical chair conforma-
The bond lengths of the indium to the oxygen atoms differ
depending on the origin of the oxygen atom revealing the non-
equivalency for the In-O bonds. Interestingly, the bond to the
neighbouring ligand is shorter than the bond to the directly
bonded one indicating a higher coordinative character. As men-
tioned above, each of the indium atoms possess a distorted octahe-
dral coordination geometry. In an ideal octahedron adjoining
atoms are perpendicular positioned to one another. In complex
11, the angles vary between 75.2° and 99.3° for In1, between
75.°1 and 102.4° for In2 and 75.6° and 99.8° for In3. Therefore,
the distortion at all three atoms is very distinct and can be
explained by the fact that covalent and coordinative bonds contrib-
ute to the complexation and varying bond strengths influence the
coordination geometry. Moreover, the resulting three octahedrons
-
OH
N
O
Cl
+
+
6 NEt3
H2O (traces)
N
N+
HEt
3
In
3
+ 3 InCl
3
OH
- 5 HNEt3Cl
HCl
O
In
O
In
-
OH
O
N
Cl
O
Cl
O
N
1
11
3
Scheme 4. Obtained product from the reaction of InCl and ligand 1.
Fig. 7. Molecular structure of the anion of 11 showing the atomic numbering scheme. The thermal ellipsoids of the non-hydrogen atoms are drawn at the 50% probability
level. Solvent molecules and hydrogen atoms are omitted for clarity except for H7A located at O7.

2
78
L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
Table 6
are connected along the edges forming a triade. This structural
motif could be considered as a subunit of the Keggin structure [46].
As mentioned above, solvents and guest molecules were found to
crystallise with the indium complex. These molecules are involved
in different intermolecular interactions in the crystal packing of 11
119
Sn MAS NMR data and results of GIAO calculations (B3PW91/ DGDZVP and 6–
19
3
11+G(2d,p)) of 1 Sn NMR shifts of 8.
a
Xb
b
Molecule
d
iso
d
11
d
22
d
33
j
8
exp.
calc.
ꢁ331.4
ꢁ331.4
ꢁ135.7
ꢁ137.4
ꢁ225.7
ꢁ223.8
ꢁ632.8
ꢁ633.1
497.1
495.7
0.64
0.65
(
see Supplementary material, Table S5). The bridging hydroxyl
group, O7–H7A, interacts with the not fully localised solvent mole-
cule THF while the chlorine atoms form intermolecular contacts of
a
Chemical shift in solid state.
Herzfeld-Berger convention [47,48],
b
X
= d11 – d33, j = 3 (d22 – diso)/X.
the C–Hꢀ ꢀ ꢀCl type. These interactions form intermolecular strands
+
3
of thecomplex along the crystallographic a axis. Finally, the [HNEt ]
ion interacts in a strong bifurcated hydrogen bond with one adjacent
DME molecule [H4ꢀ ꢀ ꢀO8 = 2.18(5) Å, N4ꢀ ꢀ ꢀO8 = 2.913(5) Å, h =
1
44(4)° and H4ꢀ ꢀ ꢀO9 = 2.43(5) Å, N4ꢀ ꢀ ꢀO9 = 3.156(5) Å, h = 144(4)°.
+
The second DME molecule is coordinated weakly to the [HNEt
ion via
C–Hꢀ ꢀ ꢀO contact (H32Aꢀ ꢀ ꢀO10 = 2.58 Å, C32ꢀꢀꢀO10 =
.368(6) Å, h = 136.2°). The non-interacting part of the second
3
]
a
3
DME molecule is disordered in two positions.
The synthesis of 11 shows the ability of the ligand system gen-
erated from 1 to stabilize the large indium atom in a rather unusual
complex geometry.
3.4. Solid state NMR measurements and chemical shift tensor analyses
Solid state NMR experiments were carried out in order to gain
insight into the electronic structure at the central atoms in 3, 5,
, 8, and 9. Quantum chemical calculations were performed to find
6
out the orientation of the principal tensor components of silicon or
tin atoms in these molecules. The experimental and calculated val-
ues are given in Table 5 and 6, the orientation of the principal ten-
sor components is shown in Fig. 8-11.
Fig. 8. Orientation of the 29Si CSA tensor principal components of 3-I.
Compound 3 crystallises with two crystallographic independent
half molecules in the asymmetric unit. Therefore two signals in the
2
9
Si CP/MAS NMR are found. The calculated values show some dif-
the following discussion. Adequate to this geometry a rather oblate
shielding tensor can be observed indicated by
-values of ꢁ0.81
5), ꢁ0.65 and ꢁ0.49 (6-I and 6-II, respectively). The principal ten-
ferences to the measured data. Nevertheless an unambiguous
assignment of the tensor components is possible. Fig. 8 shows
the spatial orientation of the tensor components for one molecule
of 3. The orientation in the other molecule is essentially the same,
therefore the discussion is limited to one of the crystallographic
independent molecules. The shielding tensor shows a more prolate
form with the principal components d11 and d22 of Si1 being
oriented nearly in plane with the two oxygen atoms in the coordi-
nation sphere of the silicon atom. With d33 the highest shielding of
the tetracoordinated silicon atom is observed perpendicular to the
oxygen atoms.
j
(
sor component d11 is orientated in both compounds along the axis
of the trigonal bipyramid, i.e. the lowest shielding of the pentaco-
ordinated silicon atom is in this direction. The higher shielded ten-
sor components d22 and d33 are situated in the trigonal plane of the
coordination polyhedra. The shielding in this coordination geome-
try might be explained with simple geometric arguments. There
are three equatorial substituents (O1, O2, C), which cause much
larger shielding than the two axial substituents. Furthermore the
axial substituents have longer bond distances to silicon than the
equatorial substituents.
There is a good agreement between calculated and experimen-
tal principal tensor components for the pentacoordinated and for
the hexacoordinated silicon compounds in Table 5. Compounds 5
and 6 should be considered as distorted trigonal bipyramids for
The orientation of the tensor components in the crystallo-
graphic independent molecule 6-II is essentially the same as in
molecule 6-I and is therefore not discussed further.
The hexacoordinated silicon compound 9 features a substan-
tially smaller anisotropy of the silicon NMR signal than the penta-
coordinated compounds. This is due to the more evenly distributed
ligand environment in the distorted coordination octahedra in 9.
This octahedron is formed by four oxygen atoms in one plane
which are supplemented by two perpendicular nitrogen atoms.
The investigation of similar hexacoordinated silicon complexes in
the literature showed that substituents with free electron pairs
influence the shielding in orthogonal direction [49]. This is also
observed at the hexacoordinated silicon atom in 9, where the nitro-
gen atoms lead to the highest shielding in perpendicular direction.
The oxygen atoms have a smaller shielding effect in perpendicular
direction since they withdraw electron density due to their higher
electronegativity. The shielding of the silicon atom shows a small
span of only 43.9 ppm. Together with the octahedral coordination
polyhedron the electron density distribution present around this
silicon atom is more spherical compared to the other complexes.
Table 5
2
9Si MAS NMR data and results of GIAO calculations (B3PW91/6-311+G(2d,p)) of 29Si
NMR shifts of compounds 3, 5, 6, and 9.
a
Xb
b
Molecule
d
iso
d
11
d
22
d
33
j
3
3
5
6
6
9
-I
exp.
calc.
exp.
calc.
exp.
calc.
exp.
0
8.9
34.5
42.7
33.0
42.3
13.0
24.5
9.3
ꢁ47.5
ꢁ40.6
ꢁ49.4
ꢁ42.8
82
0.47
0.6
0.42
0.5
83.2
82.4
85.2
-II
ꢁ2.38
7.1
21.8
ꢁ84.8
ꢁ86.9
2.1 ꢁ121.8 ꢁ134.8 136.9 ꢁ0.81
7.4 ꢁ120.2 ꢁ147.8 155.2 ꢁ0.6
-I
ꢁ101.1
ꢁ27.2 ꢁ127.4 ꢁ148.7 121.5 ꢁ0.65
ꢁ24.1 ꢁ125.6 ꢁ153.5 129.3 ꢁ0.6
ꢁ24.5 ꢁ119.3 ꢁ151.6 127.1 ꢁ0.49
ꢁ17.9 ꢁ115.9 ꢁ158.8 141.0 ꢁ0.4
calc. ꢁ101.1
-II
exp.
calc.
exp.
ꢁ98.5
ꢁ97.5
ꢁ172.4
ꢁ147.9 ꢁ177.4 ꢁ191.8
ꢁ148.7 ꢁ183.9 ꢁ196.7
43.9 ꢁ0.34
48.0 ꢁ0.5
calc. ꢁ176.5
a
Chemical shift in solid state.
Herzfeld-Berger convention [47,48],
b
X = d11 – d33, j = 3 (d22 – diso)/X.

L.E.H. Paul et al. / Inorganica Chimica Acta 423 (2014) 268–280
279
Fig. 9. Orientation of the 29Si CSA tensor principal components of 5 and 6-I.
Fig. 10. Orientation of the 29Si CSA tensor principal components of 9.
Fig. 11. Orientation of the tensor components in 8.
For complex 8 a 119Sn solid state NMR spectrum was measured.
The values determined for the chemical shift tensors are listed in
Table 6. The lower shielding tensor components d11 and d22 lie in
the same plane as the tridentate ligand 1 (Fig. 11). The highest
shielding d33 is perpendicular to that plane. d11 points along the
O–Sn–O axis and d22 towards the Sn–N bond. In contrast, shielding
independent molecules: C10–Si1–C16 101.4(1)°, O1–Si1–O2
133.8(1)°, C31–Si2–C37 103.3(1)° and O3–Si2–O4 132.6(1)°. The
orientation of the tensor components in 6 was explained with a
trigonal bipyramidal coordination geometry of the silicon atoms
d
33 runs parallel to the free electron pairs located at the oxygen
with the parameter
The larger bond angles in 8 lead to a distorted coordination
geometry with = 0.55. If one considers this as a strong distorted
trigonal bipyramid, then the atoms O1–Sn1–O2 form the axis of
the bipyramid. The lowest shielding (d11) is in this direction. The
highest shielding tensor components d33 is again in the trigonal
plane of the bipyramid, which is in line with the discussion of
the tensor components in 5 and 6, but together with a d22 showing
a significantly smaller shielding contribution for the Sn complex
indicating the stronger deviation from the trigonal bipyramid in 8.
s = 0.59.
atoms O1 and O2 and the -electrons of the nitrogen atom. In
p
contrast to the pentacoordinated silicon complexes 5 and 6, the
shielding tensor shows a more prolate form and the orientation of
the principal components found here is different to orientation pat-
tern in 5 and 6 (see above). This fact is explained with the different
coordination geometry found in this complex. The angle C10–Sn1–
C16 is 125.85(5)° and the angle O1–Sn1–O2 159.13(5)°. These are
larger angles than in the comparable silicon compound 6. Therein
the following angles were observed for the two crystallographic
s

2
80
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