Synthesis and characterisation of 5, 5′-bistetrazolate salts with alkali metal, ammonium and imidazolium cations

Article abstract of DOI:10.1002/zaac.201300150

We report on the synthesis and characterisation of the alkali metal 5, 5'-bistetrazolate (BT^2-) salts Li₂BT (1), Na₂BT (2), K₂BT (3), Rb₂BT (4) and Cs₂BT (5) as well as the mono ammonium (9) and the mono (10) and bis(1-ethyl-3-methylimidazolium) (11) salts of 5, 5'-bistetrazole. The crystal structures of the hydrates of the alkali metal salts (1h-4h) and hydrate free (9) to (11) are presented. Additionally we present structures of the monocaesium 5, 5'-bistetrazolate (6) and alternative modifications of the known salts barium (7h) and diammonium (8) 5, 5'-bistetrazolate. Among the presented compounds are the first reversibly melting 5, 5'-bistetrazolate salts (10, 11) and also the first ionic liquid on the basis of 5, 5'-bistetrazole (11). All substances were investigated by NMR and IR spectroscopy, elemental analysis and combined TGA/DSC measurements. Corresponding to our main motive, the evaluation of the coordination behaviour of 5, 5'-bistetrazole, we give a short summary of the metal 5, 5'-bistetrazole salts structurally characterised so far. Copyright

Full text of DOI:10.1002/zaac.201300150

Job/Unit: Z13150
/KAP1
Date: 21-05-13 16:49:20
Pages: 14
ARTICLE
DOI: 10.1002/zaac.201300150
Synthesis and Characterisation of 5,5’-Bistetrazolate Salts with Alkali Metal,
Ammonium and Imidazolium Cations
Lars H. Finger,[a] Fabian G. Schröder,[a] and Jörg Sundermeyer*[a]
Dedicated to Professor Heinrich Nöth on the Occasion of His 85th Birthday
Keywords: Alkali metals; 5,5’-Bistetrazolate salts; Crystal structures; Coordination chemistry; Ionic liquids
Abstract. We report on the synthesis and characterisation of the alkali
nium (8) 5,5’-bistetrazolate. Among the presented compounds are the
metal 5,5’-bistetrazolate (BT2–) salts Li2BT (1), Na2BT (2), K2BT (3), first reversibly melting 5,5’-bistetrazolate salts (10, 11) and also the
Rb2BT (4) and Cs2BT (5) as well as the mono ammonium (9) and the first ionic liquid on the basis of 5,5’-bistetrazole (11). All substances
mono (10) and bis(1-ethyl-3-methylimidazolium) (11) salts of 5,5’-
bistetrazole. The crystal structures of the hydrates of the alkali metal
salts (1h–4h) and hydrate free (9) to (11) are presented. Additionally
were investigated by NMR and IR spectroscopy, elemental analysis
and combined TGA/DSC measurements. Corresponding to our main
motive, the evaluation of the coordination behaviour of 5,5’-bistetra-
we present structures of the monocaesium 5,5’-bistetrazolate (6) and zole, we give a short summary of the metal 5,5’-bistetrazole salts struc-
alternative modifications of the known salts barium (7h) and diammo-
turally characterised so far.
Intrigued by the first detailed description of the rare earth
metal salts, we wanted to further investigate the coordination
behaviour of 5,5’-bistetrazole. We chose the alkali metal salts
as a first model system. Our special interest concerned the
question if a chelating coordination mode is dependent on the
cation size. In addition we specifically wanted to analyse the
sodium and the barium salt of 5,5’-bistetrazole which have
been utilised in the synthesis of the free acid and the rare earth
metal salts, respectively. During our literature research we
were surprised to find that the monoammonium salt of 5,5’-
bistetrazole is regarded a promising gas generating compound
used in airbag systems.[5b] We wished to prepare and investi-
gate this compound to evaluate in which way it deviates from
similar substances. Finally we were interested if the 5,5’-biste-
trazolate anion can be employed in organic salts with weakly
coordinating cations. The specific aim was to prepare unusual
ionic compounds in which an isolated 5,5’-bistetrazolate di-
anion is present.
Introduction
The first synthesis of 5,5’-bistetrazole (H2BT) was already
reported at the beginning of the 20th century.[1] The potential
of this nitrogen-rich compound as an explosive was noticed
soon.[2] Friederich developed a novel synthesis for the title
compound which no longer utilised handling of the highly haz-
ardous reactants cyanogen and hydrazoic acid in aqueous solu-
tions.[3] This procedure was improved and simplified by Nel-
son et al.[4] Whereas 5,5’-bistetrazole and its derivatives have
been intensively studied regarding their energetic properties
and numerous patents claim their use in explosive composi-
tions,[5] very little is known about the coordination behaviour
of this intriguing ligand. Steel et al. were the first to publish
three transition metal complexes in 1995 and presented also
the crystal structure of the free acid.[6] The group of Klein
prepared and characterised several rare earth metal salts,[7]
Klapötke et al. presented a series of alkaline earth metal salts[8]
and the first structurally characterised transition metal salt.[9]
Combinations of 5,5’-bistetrazole with nitrogen-rich cations
such as ammonium, hydrazinium, guanidinium and related
have been investigated most recently by Klapötke et al. and
also Shreeve et al.[10]
We wish to report herein on the synthesis and characterisa-
tion including single crystal XRD structure determination of a
series of alkali metal salts, the monoammonium salt and two
1-ethyl-3-methylimidazolium salts of 5,5’-bistetrazole. Ad-
ditionally we want to present alternative crystal structure modi-
fications of the previously described barium and diammonium
5,5’-bistetrazolate.
* Prof. Dr. J. Sundermeyer
Fax: +49-64-21-2825711
E-Mail: jsu@chemie.uni-marburg.de
[a] Fachbereich Chemie
Results and Discussion
Philipps-Universität Marburg
Hans-Meerwein-Str. 4
Synthesis
35032 Marburg, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201300150 or from the au-
thor.
The high acidity of 5,5’-bistetrazole[11] allows the prepara-
tion of alkali metal salts starting from the respective metal
Z. Anorg. Allg. Chem. 0000, ᭿,(᭿), 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. H. Finger, F. G. Schröder, J. Sundermeyer
ARTICLE
hydroxide or carbonate. This route was also employed for the
barium salt. The dilithium (1h) and dirubidium (4h) salts crys-
tallised from hot water with two, the disodium (2h) and barium
(7h) salts with five water molecules per molecular unit
(Scheme 1) and were characterised by XRD. The dipotassium
(3) and dicaesium (5) salts usually crystallised without hy-
drating water molecules in the structure. Both compounds have
not afforded publishable structure solutions so far, though. In-
stead the single crystal structures of dipotassium 5,5’-bistetra-
zolate dihydrate (3h) and monocaesium 5,5’-bistetrazolate
(CsHBT, 6) are presented. In each case also the water-free
phase was prepared and investigated. Water-free Li2BT is
highly hygroscopic.
Scheme 2. Synthesis of monoammonium (9) and mono (10) and di
(11) (1-ethyl-3-methyl-imidazolium) 5,5Ј-bistetrazolate.
SIR2004[15] or SUPERFLIP,[16] refined with SHELXL-97[17]
and finally validated using PLATON[18] software, all within
the WinGX[19] software bundle. Absorption corrections where
either applied within WinGX (multi-scan[20] or gaussian[21]) or
beforehand within the APEX2 software (multi-scan).[22]
Graphic representations were created using Diamond 3.[23] C-
bound hydrogen atoms were constrained to parent site; hydro-
gen atoms on heteroatoms were located in the Fourier map
and refined independently. In all graphics the displacement el-
lipsoids are shown for the 50% probability level, hydrogen
atoms are shown with arbitrary radius. Selected crystal data
and experiment parameters are listed in Table 1 and Table 2.
Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-927399, -927400, -927401, -927402,
-927403, -927404, -927405, -927406, -927407, -927408. Cop-
ies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
+44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk; http://
www.ccdc.cam.ac.uk/cgi-bin/catreq.cgi].
Scheme 1. Synthesis of alkali metal 5,5Ј-bistetrazolates (3) and (5),
the hydrates (1h), (2h) and (4h) and barium 5,5Ј-bistetrazolate penta-
hydrate (7h).
Monoammonium 5,5’-bistetrazolate ((NH4)HBT, 9) was
prepared by reacting equimolar amounts of 5,5’-bistetrazole
and diammonium 5,5’-bistetrazolate ((NH4)2BT, 8). To our
surprise the crystallisation of this mixture by cooling a boiling
aqueous solution to room temperature yielded again (NH4)2BT
(8) as evidenced by 13C-NMR spectroscopy, elemental analysis
and XRD unit cell determination. Only if the remaining solu-
tion is decanted and cooled further to 4 °C, the monoammon-
ium 5,5’-bistetrazolate crystallises.
Mono(1-ethyl-3-methylimidazolium)
5,5’-bistetrazolate
((EMIM)HBT, 10) was prepared by combining barium 5,5’-
bistetrazolate and 1-ethyl-3-methylimidazolium bisulfate in
water. Bis(1-ethyl-3-methylimidazolium) 5,5’-bistetrazolate
(EMIM2BT, 11) was synthesised by reacting 5,5’-bistetrazole
with EMIM carbonate in dry methanol (Scheme 2). The prod-
uct EMIM2BT is again highly hygroscopic.
Dilithium 5,5’-bistetrazolate dihydrate (Li2BT·2H2O, 1h)
¯
crystallised in the triclinic space group P1 with a single mole-
cule in the unit cell and half a molecule in the asymmetric
unit. The bond lengths in the tetrazole moiety are in the same
range as values which have been found in the free 5,5’-biste-
Molecular Structures
The data collection for the single crystal structure determi- trazole acid[6b] and published 5,5’-bistetrazolate salts.[7–10]
nations was performed with a Stoe IPDS-II or a Bruker
The N2–N3 distance is generally the shortest whereas N1–
D8 QUEST diffractometer by the X-ray service department of N2 and N3–N4 are the longest bonds. The observed bond
the Fachbereich Chemie, University of Marburg. The Stoe lengths lie between typical values for N–N single (1.366 Å)
IPDS-II device is equipped with a Mo-Kα X-ray source (λ = and N=N double (1.300 Å) bonds in heterocyclic aromatic sys-
0.71073 Å), graphite mono-chromator and active imaging tems. The observed C–N distances show evenly good agree-
plate. Stoe IPDS software (X-AREA) was used for data collec- ment with bond lengths in common aromatic heterocycles
tion, cell refinement and data reduction, respectively.[12] The (1.331 Å (pyrazole), 1.338 Å (pyridine)).[24] A tabular com-
D8-QUEST is equipped with a Mo-Kα X-ray micro source parison of bond lengths and angles in the bistetrazole moiety of
(Incotec), a fixed chi goniometer and a PHOTON 100 CMOS all presented structures is given in the Supporting Information.
detector. Bruker software (Bruker Instrument Service, APEX2,
The bistetrazole moiety in structure 1h is perfectly planar
SAINT) was used for data collection, cell refinement and data and builds almost planar chains in which bistetrazolate and
reduction.[13] The structures were solved with SIR-97,[14] lithium ions are alternating (Figure 1). The lithium atoms are
2
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5,5’-Bistetrazolate Salts with Alkali Metal, Ammonium and Imidazolium Cations
Table 1. Selected crystallographic data for compounds 1h to 4h and 6.
Li2BT·2H2O (1h)
Na2BT·5H2O (2h)
K2BT·2H2O (3h)
Rb2BT·2H2O (4h)
CsHBT (6)
Formula
C2H4Li2N8O2
186.01
C2H10N8Na2O5
272.16
C2H4K2N8O2
250.33
Monoclinic
P21/c
colourless block
0.21 ϫ 0.09 ϫ 0.09
3.8505(4)
11.3156(12)
9.7354(10)
90
93.006(9)
90
423.59(8)
2
1.963
11.08
C2H4N8O2Rb2
343.08
Monoclinic
P21/c
colourless block
0.33 ϫ 0.13 ϫ 0.09
4.0884(2)
11.3281(7)
9.9483(6)
90
93.510(5)
90
459.88(5)
2
2.478
106.32
C2H1Cs1N8
270.02
Monoclinic
Pc
colourless block
0.32 ϫ 0.12 ϫ 0.05
4.6222(4)
8.6949(6)
16.2896(17)
90
94.123(8)
90
652.98(10)
4
2.747
56.11
FW /g·mol–1
Crystal system
Space group
Colour, habit
Triclinic
Triclinic
¯
¯
P1
P1
colourless block
colourless block
0.83 ϫ 0.61 ϫ 0.41
7.2089(6)
7.4623(6)
10.7752(8)
81.333(3)
76.478(3)
67.604(3)
519.85(7)
2
Crystal size /mm 0.13 ϫ 0.08 ϫ 0.07
a /Å
b /Å
c /Å
α /°
β /°
3.3677(8)
7.3623(2)
7.5007(2)
82.897(18)
87.120(19)
80.761(18)
182.06(4)
1
1.679
1.38
94
100(2)
γ /°
V /Å3
Z
Dcalc /g·cm–3
μ /cm–1
F(000)
T / K
1.739
2.23
280
100(2)
252
100(2)
324
100(2)
496
100(2)
θ range /°
h, k, l range
Refl. Coll.
Refl. Indep.
Refl. I Ͼ 2σ(I)
2.74 : 26.69
–4:4, –9:9, –9:9
1476
762
602
2.96 : 27.17
–9:8, –9:9, –13:13
6166
2310
1952
2.76 : 26.72
–4:4, –12:14, –12:12
2267
893
778
2.73 : 26.72
–5:5, –14:14, –12:12
5725
973
888
2.34 : 26.67
–5:5, –10:10, –18:20
3188
2313
2152
Data/ rest./ param. 762 / 2 / 72
2310 / 1 / 194
0.0616
0.0532
0.1386
1.047
893 / 0 / 72
0.0244
0.0224
0.0546
0.987
973 / 0 / 72
0.0575
0.0210
0.0492
1.047
2313 / 4 / 209
0.0473
0.0266
0.0629
0.999
Rint
0.0287
0.0349
0.0872
0.968
R1 (obs)
wR2 (all)
GooF (F2)
CCDC
927399
927400
927401
927402
927403
Table 2. Selected crystallographic data for compounds 7h and 8 to 11.
BaBT·5H2O (7h)
(NH4)2BT (8)
(NH4)HBT (9)
(EMIM)HBT (10)
(EMIM)2BT (11)
Formula
C2H10BaN8O5
363.52
C2H8N10
172.18
Orthorhombic
Pban
colourless block
0.18 ϫ 0.16 ϫ 0.14
9.1301(10)
10.7631(13)
3.6660(6)
90
90
90
360.25(8)
2
1.587
C2H5N9
155.15
Monoclinic
P21/c
colourless needle
0.66 ϫ 0.10 ϫ 0.07
4.5136(6)
8.4692(12)
15.522(2)
90
94.320(6)
90
591.67(14)
4
1.742
1.37
C8H12N10
248.28
Monoclinic
P21/n
colourless block
0.17 ϫ 0.15 ϫ 0.12
4.5978(3)
18.9191(11)
13.0052(7)
90
94.586(4)
90
1127.65(12)
4
1.462
1.05
C14H22N12
358.44
Monoclinic
P21/n
colourless block
0.27 ϫ 0.23 ϫ 0.16
9.8020(6)
7.9782(6)
12.0450(8)
90
108.716(5)
90
892.13(10)
2
1,334
0.92
FW /g·mol–1
Crystal system
Space group
Colour, habit
Triclinic
¯
P1
colourless block
Crystal size /mm 0.21 ϫ 0.13 ϫ 0.08
a /Å
b /Å
c /Å
α /°
β /°
7.4404(7)
8.1615(7)
9.2594(9)
88.638(8)
73.671(7)
88.933(7)
539.40(9)
2
2.238
37.07
348
100(2)
γ /°
V /Å3
Z
Dcalc /g·cm–3
μ /cm–1
F(000)
T / K
1.24
180
100(2)
320
100(2)
520
100(2)
380
100(2)
θ range /°
h, k, l range
Refl. Coll.
Refl. Indep.
Refl. I Ͼ 2σ(I)
2.29 : 26.68
–9:9, –10:10, –11:11
6259
2289
2073
2.93 : 26.70
–10:11, –13:13, –4:4
2935
392
319
2.63 : 27.08
–5:4, –10:10, –19:19
3538
1302
1025
1.90 : 26.71
–5:5, –23:20, –16:14
7731
2383
1470
2.34 : 26.72
–10:12, –12:10, –15:15
7475
1882
1355
Data/ rest./ param. 2289 / 12 / 185
392 / 0 / 37
0.0382
0.0273
0.0661
0.939
1302 / 0 / 124
0.0448
0.0517
0.0970
1.211
2383 / 0 / 169
0.0528
0.0337
0.0696
0.781
1882 / 0 / 120
0.0429
0.0339
0.0843
0.893
Rint
0.0471
0.0226
0.0547
0.989
R1 (obs)
wR2 (all)
GooF (F2)
CCDC
927404
927405
927406
927407
927408
Z. Anorg. Allg. Chem. 0000, 0–0
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ARTICLE
coordinated in a tetrahedral fashion by two oxygen and two
nitrogen atoms with bond angles ranging from 104.1(1)° to
115.5(1)°. In the crystal structure the chains are stacked and
connected over lithium oxygen bonds, the stacks (Figure 2) are
held together by strong hydrogen bonds (O1IV···N3:
2.785(2) Å).
Figure 3. Dimeric units in disodium 5,5Ј-bistetrazolate pentahydrate
(2h); selected bond lengths /Å and angles /°: C1–C2I: 1.463(2), C1–
N1: 1.341(2), N1–N2: 1.349(2), N2–N3: 1.320(2), N3–N4: 1.354(2),
C1–N4: 1.338(2), C2–N5: 1.342(2), N5–N6: 1.351(2), N6–N7:
1.315(2), N7–N8: 1.346(2), C2–N8: 1.338(2), N1–Na1: 2.408(2), N8–
Na1: 2.450(2), N7–Na2: 2.556(2), O1–Na1: 2.377(2), O4–Na1:
2.473(2), O5–Na1: 2.351(2), O5I–Na1: 2.380(2), O1–Na2: 2.345(2),
O2–Na2: 2.355(2), O3–Na2: 2.357(2), O3II–Na2: 2.524(2), O4–Na2:
2.407(2), O3II···N2: 2.968(2), N1–Na1–N8: 178.0(1), N7–Na2–O3II:
I
II
147.0(1); symmetry operations: = 1–x, –y, 1–z, = –x, –y, 2–z.
Figure 1. Chain structure in dilithium 5,5Ј-bistetrazolate dihydrate
(1h); selected bond lengths /Å and angles /°: C1–C1I: 1.468(3), C1–
N1: 1.335(2), N1–N2: 1.347(2), N2–N3: 1.316(2), N3–N4: 1.345(2),
C1–N4: 1.335(2), N1–Li1II: 2.060(3), N2–Li1: 2.034(3), O1–Li1:
1.991(3), O1III–Li1: 2.012(3), O1II···N4I: 2.786(2), O1IV···N3:
2.785(2), O1–Li1–N2: 115.5(1), N2–Li1–N1II: 111.0(1), O1–Li1–
O1III: 114.6(2), N1II–Li1–O1IV: 104.1(1); symmetry operations: I = 1 –
II
III
IV
x, –y, 2 –z, = 1 –x, 1 –y, 2 –z, = –1+x, y, z, = 2 –x, 1 –y, 1 –z.
Figure 4. Stacked structure of dimeric units in Na2BT·5H2O (2h), hy-
¯
drogen atoms are omitted for clarity; viewing direction [120].
The potassium salt exhibits a special behaviour concerning
crystallisation. In multiple attempts the water-free substance
could be crystallised. This could be proven by IR spectroscopy,
elemental analysis and XRD single crystal analysis. The re-
sulting structure solution clearly evidences the water-free
phase but does not allow any discussion of bond lengths due
to bad crystal quality. In one instance the chosen crystal turned
out to be a dihydrate of the respective salt whose solution is
presented here. Dipotassium 5,5’-bistetrazolate dihydrate (3h)
crystallised in the space group P21/c with four asymmetric
units consisting of half a molecule per unit cell. The potassium
atom is coordinated by five nitrogen and three oxygen atoms
forming a doubly capped trigonal prism (Figure 5).
In one case the potassium atom is coordinated in a distorted
chelating fashion (between N4III and N1V) with an angle of
57.24(3)° at the central atom. The potassium atom is not in
plane with the chelating NCCN fragment, though. Potassium
nitrogen distances range from 2.916(1) Å (N2II) to 2.977(1) Å
(N2) and are in good agreement with distances found in the
potassium tetrazolate.[25] The K1–N1V distance (3.211(1) Å) is
considerably longer than typical K–N bonds but can still be
regarded as a coordinating bond. Similar distances have been
Figure 2. Chain stacking in the crystal structure of dilithium 5,5Ј-bis-
tetrazolate dihydrate (1h); view along the b axis.
¯
Na2BT·5H2O (2h) crystallised in the space group P1 with
two molecular units per elementary cell and one molecule per
asymmetric unit. The sodium atoms are six fold coordinated
in an octahedral fashion. Na1 is surrounded by two nitrogen
and four oxygen atoms, Na2 by one nitrogen atom and five
oxygen atoms, the coordination polyhedron around Na2 is con-
siderably distorted. Sodium nitrogen distances range from
2.408(2) Å (N1–Na1) to 2.556(2) Å (N7–Na2), sodium oxygen
bond lengths lie between 2.345(2) Å (O1–Na2) and 2.473(2) Å
(O4–Na1). Dimeric entities prevail in which two bistetrazolate
moieties are linked by two sodium atoms (Figure 3). When
viewing along the line which is connecting the dimers (direc-
¯
tion [120]) a stacked structure appears (Figure 4).
4
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5,5’-Bistetrazolate Salts with Alkali Metal, Ammonium and Imidazolium Cations
Figure 7. Coordination of the rubidium atoms in dirubidium 5,5Ј-biste-
trazolate dihydrate (4h); selected bond lengths /Å and angles /°: C1–
C1I: 1.457(4), C1–N1: 1.340(3), N1–N2: 1.347(3), N2–N3: 1.317(3),
N3–N4: 1.346(2), C1–N4: 1.340(3), Rb1–N2: 3.101(2), Rb1–N2II:
3.046(2), Rb1–N4III: 3.035(2), Rb1–N4IV: 3.087(2), Rb1–N1V:
Figure 5. Coordination of the potassium atoms in dipotassium 5,5Ј-
bistetrazolate dihydrate (3h); selected bond lengths /Å and angles /°:
C1–C1I: 1.457(3), C1–N1: 1.335(2), N1–N2: 1.351(2), N2–N3:
1.315(2), N3–N4: 1.348(2), C1–N4: 1.341(2), K1–N2: 2.977(1), K1–
N2II: 2.916(1), K1–N4III: 2.922(1), K1–N4IV: 2.949(1), K1–N1V:
3.211(1), K1–O1: 2.760(1), K1–O1VI: 2.892(1), K1–O1VII: 2.860(1),
O1VI···N3II: 2.823(2), O1VII···N1V: 2.844(2), N4III–K1–N1V: 57.24(3);
3.238(2), Rb1–O1: 2.941(2), Rb1–O1VI
: :
3.016(2), Rb1–O1VII
2.997(2), O1VI···N3II: 2.844(3), O1VII···N1V: 2.872(3), N4III–Rb1–N1V:
I
II
III
55.63(5); symmetry operations: = –x, –y, –z, = 1+x, y, z, = 1+x,
IV
V
VI
0.5–y, 0.5+z,
= x, 0.5–y, 0.5+z, = –x, 0.5+y, 0.5–z,
= 1 –x,
I
II
III
VII
symmetry operations: = 1–x, 1–y, –z, = 1+x, y, z,
= x, 0.5–y,
1–y, –z,
= –1+x, y, z.
IV
V
VI
0.5+z, = 1–x, 0.5–y, 0.5+z, = 1–x, –0.5+y, 0.5–z, = 2–x, –y, –z,
VII
= –1+x, y, z.
the related salts of 1H-tetrazole[25] and 5-aminotetrazole[27]
with respect to alkali metal nitrogen and alkali metal oxygen
bond lengths.
observed in potassium phenanthroline complexes.[26] The
packing in the crystal structure is dominated by a wave like
topology (viewing along the c axis) in which layers of 5,5’-
bistetrazolate dianions alternate with layers consisting of po-
tassium atoms and water molecules (Figure 6).
Figure 8. Wave-like structure in dirubidium 5,5Ј-bistetrazolate dihy-
drate (4h); hydrogen atoms are omitted for clarity.
Figure 6. Wave-like topology in dipotassium 5,5Ј-bistetrazolate dihy-
drate (3h); view along the c axis; hydrogen atoms are omitted for
clarity.
Dicaesium 5,5’-bistetrazolate could be crystallised from
aqueous solution in the form of colourless blocks. However,
XRD experiments led to several analogous data sets for which
Dirubidium 5,5’-bistetrazolate dihydrate (4h, Figure 7) crys- no reasonable solution could be generated so far. In one case
tallised in the monoclinic space group P21/c with four asym- instead of the dicaesium salt a crystal of monocaesium 5,5’-
metric units consisting of half a molecule per unit cell. It is bistetrazolate (6) was investigated. Compound 6 crystallised in
isostructural, although according to the XRD results enantio- the monoclinic space group Pc with two asymmetric entities
meric, to the potassium salt.
per unit cell (Figure 9). The asymmetric unit consists of two
The Rb–N distances range from 3.035(2) Å (Rb1–N4III) to molecular units. PLATON suggests the space group P21/c on
3.238(2) Å (Rb1–N1V) in the longest case. Rubidium oxygen the basis of an additional inversion centre. However, neither
distances deviate between 2.941(2) Å (Rb1–O1) and in P21/c nor in P2/c, a reasonable refinement is possible, and
3.016(2) Å (Rb–O1VI). As in the potassium salt (3h) a wave- the expected extinction of reflexes for the 21 axis is not pres-
like structure is visible, when viewing along the c axis (Fig- ent. The suggestion by PLATON has therefore to be attributed
ure 8). The tilting angle between the 5,5’-bistetrazolate moie- to a pseudo inversion centre. Additionally a partial mix of
ties is higher, though (59.1° in (4h) compared to 52.3° in (3h)). enantiomers is present in the structure; a TWIN refinement has
The presented structures show an overall good agreement with been applied resulting in a freely refined BASF value of
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0.3935. The asymmetric unit consists of two caesium atoms
and two 5,5’-bistetrazole moieties with a single proton remain-
ing in each case.
Figure 12. Molecular unit of barium 5,5Ј-bistetrazolate pentahydrate
(7h); selected bond lengths /Å and angles /°: C1–C2: 1.459(4), C1–
N1: 1.342(4), N1–N2: 1.341(4), N2–N3: 1.322(4), N3–N4: 1.352(4),
C1–N4: 1.334(4), C2–N5: 1.341(4), N5–N6: 1.348(4), N6–N7:
1.319(4), N7–N8: 1.343(4), C2–N8: 1.335(4), N5–Ba1: 2.971(3), N6I–
Ba1: 2.961(3), N7II–Ba1: 2.946(3), O1–Ba1: 2.782(2), O2–Ba1:
2.700(3), O3–Ba1: 2.871(2), O3II–Ba1: 2.805(2), O4–Ba1: 2.860(2),
O4I–Ba1: 2.816(3), O1···N1: 2.782(4), N5–Ba1–N6I: 116.2(1), N6I–
I
Ba1–N7II: 113.8(1); symmetry operations: : 2–x, 2–y, 1–z, II: 1–x, 2–
Figure 9. Molecular structure of caesium 5,5Ј-bistetrazolate (6), the
isolated atoms N11I, N12I and N14II belong to respective tetrazole
rings which are not displayed to avoid an overcrowding of the picture;
selected bond lengths /Å and angles /°: N1–Cs1: 3.183(9), N5–Cs1:
3.318(9), N6I–Cs1: 3.337(7), N14II–Cs1: 3.388(8), N15III–Cs1:
3.400(10), N3II–Cs1: 3.268(9), N12I–Cs1: 3.221(8), N11–Cs1:
3.333(8), N10–Cs2: 3.308(10), N11I–Cs2: 3.257 (8), N3II–Cs2:
3.251(6), N4III–Cs2: 3.295(9), N8III–Cs2: 3.205(9), N14IV–Cs2:
3.341(8), N13V–Cs2: 3.293(8), N6VI–Cs2: 3.322(9), N7VI···N9:
2.728(11), N16III···N2II: 2.709(11), N1–Cs1–N5: 53.6(2), N4III–Cs2–
y, 1–z, III: –1+x, y, z.
I
III
N8III: 53.9(2); symmetry operations: :1+x, y, z, II: x, 1–y, 0.5+z,
:
1+x, 1–y, 0.5+z, IV: 1+x, 2–y, 0.5+z, V: x, 2–y, 0.5+z, VI: 1+y, 1+y, z.
The coordination polyhedra around the caesium atoms ap-
proximate doubly capped trigonal prisms. Cs–N distances
range from 3.183(9) Å to 3.400(10) Å and compare well to
related substances.[25,28] In two cases the 5,5’-bistetrazolate li-
gand coordinates in a chelating fashion (N1–Cs1: 3.183(9) Å,
N5–Cs1: 3.318(9) Å, N4III–Cs2: 3.295(9) Å, N8III–Cs2:
3.205(9) Å). In these cases the pentacycle from two carbon,
two nitrogen and one caesium atom is almost planar. In com-
parison to the potassium (3h) and rubidium salts (4h) the che-
lating angles are further decreased (N1–Cs1–N5: 53.6(2)°,
N4III–Cs2–N8III: 53.9(2)°]. It is noteworthy that in multiple
cases not only a single atom of a respective tetrazole ring lies
in bonding distance to the caesium atom, but two neighbouring
atoms show very similar distances (most prominent: N12I–
Cs1: 3.221(8) Å and N11I–Cs1: 3.225(8) Å). A η2-bonding sit-
uation might be considered, but the unchanged bond lengths
in the tetrazole rings contradict a participation of the π-orbitals
in the coordination. The same phenomenon was observed with
the caesium tetrazolate[25] and the caesium cyanotetrazol-
ate.[28]
Figure 10. Hydrogen-bonded chains of 5,5Ј-bistetrazolate in the crys-
tal structure of caesium 5,5Ј-bistetrazolate (6); view along the a axis.
Figure 11. Crystal structure of caesium 5,5Ј-bistetrazolate; view along
[210]; stacked chains are tilted against each other by 90°.
In the crystal structure hydrogen bonded chains of
Barium 5,5’-bistetrazolate has been described previously as
5,5’-bistetrazolate (N7VI···N9: 2.728(11) Å, N16III···N2II: a tetrahydrate.[8,29] We found it to crystallise as a pentahydrate
¯
2.709(11) Å) prevail, between which the caesium atoms are (7h) in the space group P1 with two molecular entities per
located (Figure 10). The chains are tilted by 90° with respect to unit cell. The structure is very similar to the already known
neighbouring chains and arranged in stacks (viewing direction modification. The barium atom is coordinated ninefold in a
[210]). Within the stacks the chains are shifted with respect to triply capped trigonal prism by six oxygen and three nitrogen
each other so that every fifth chain is analogous (Figure 11).
atoms (Figure 12). O–Ba distances range from 2.700(3) Å
6
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5,5’-Bistetrazolate Salts with Alkali Metal, Ammonium and Imidazolium Cations
(O2–Ba1) to 2.871(2) Å (O3–Ba1), nitrogen barium bond Na+ (1.16 Å, CN6) are not coordinated in a chelating fashion,
lengths are 2.971(3) Å (N5–Ba1), 2.961(3) Å (N6II–Ba1) and the larger alkali metal ions are chelated by the 5,5’-bistetrazol-
2.946(3) Å (N7III–Ba1).
ate moiety. In the case of the potassium and the rubidium salt,
Zigzag chains of barium atoms which are connected over the chelation is less pronounced, as the metal atoms are not in
two water molecules (the trigonal prisms share edges) and the plane with the 5,5’-bistetrazolate moiety. So far all atoms ex-
bistetrazole moieties filling the cavities between the chains are cept Ba2+ which have an ionic radius above 1.26 Å are che-
a main motive in both crystal structures (Figure 13a). The ad- lated; the ones with smaller radii are not. We are convinced
ditional water molecule in the present structure does not coor- that this effect is of course on the one hand affected by the
dinate to the barium atom. Its position in the crystal becomes increasing Lewis acidity of the cations with decreasing radius
evident when the structure is viewed along the a axis (Fig- and therefore preferred coordination by water, but on the other
ure 13b). Situated between chains of barium atoms and the ad- hand can also be attributed to the rigid nature of the bicyclic
jacent bistetrazole moieties it connects the chains over strong ligand. Very small cations considerably increase the chelating
hydrogen bonds (O5···N2: 2.815(4) Å, O5···O1: 2.775(3) Å). angle and thereby decrease the C–N–M angle in the metalla-
These are not the only hydrogen bonds, almost every OH-bond pentacycle. Open chelating ligands like oxalic acid can easily
is participating in a strong network of H-bonds constraining balance this by decreasing the distance between the coordinat-
the crystal structure.
ing atoms which is less easily possible for the bicyclic 5,5’-
bistetrazolate. A considerable decrease of the C–N–M angle
will lead to less orbital overlap between the anionic lone pairs
of the nitrogen atoms and the metal orbitals, which we believe
to be the reason why small atoms are chelated less likely. The
only exception to this trend is the copper(II) salt.[9] Despite
having a very small ionic radius of 0.87 Å (CN6) it is chelated
by 5,5’-bistetrazole. The differences in bond lengths indicate,
though, that only one of the chelating atoms forms a strong
ionic bond (2.027(4) Å) whereas the other one only forms a
weak coordinative bond (2.760(5) Å). The chelating angles N–
M–N follow a distinct and natural trend by increasing with
the cation becoming smaller. In Table 3 the ionic radii of the
respective metal ions are opposed to the coordination mode
and if applicable the chelating angle.
The structure of the diammonium 5,5’-bistetrazolate (8) was
described previously with a monoclinic cell.[10a] During our
own independent research we were able to confirm this struc-
ture, but also observed a second orthorhombic modification. In
this case (NH4)2BT (8) crystallised in the space group Pban
with two molecules in the unit cell but only a quarter molecule
in the asymmetric unit (Figure 14). In contrast to the known
structure in which the bistetrazolate moiety is perfectly planar,
here the tetrazole rings are strongly tilted against each other
(N1–C1–C1I–NIV: 35.6(1)°).
In both crystal structures a layered topology is prominent.
Viewing along the c axis a picture almost indistinguishable
from the previously reported structure appears (Figure 15a).
Bistetrazolate moieties are connected over the ammonium ions
via a hydrogen-bonding network. Only when viewing the
structure along the b axis a considerable difference becomes
visible. Whereas in the structure described by Klapötke et al.
the bistetrazolate anions are ordered in a stair like fashion here
they are completely coplanar in each layer (Figure 15b).
The monoammonium salt of 5,5’-bistetrazole crystallised in
the monoclinic space group P21/c with four molecules per unit
cell. The asymmetric unit consists of one ammonium cation
and two symmetrically non-equivalent tetrazole rings. The re-
maining proton is disordered over the positions H1 and H2
with site occupation factors of roughly 50% (Figure 16). The
Figure 13. Crystal structure of 7h; a) Zigzag chains of barium atoms;
view in b direction; b) barium chains and adjacent bistetrazolate anions
connected over the fifth water molecule; view in a direction; hydrogen
atoms other than those on O5 are omitted for clarity.
When comparing the ionic radii of the metal atoms in 5,5’-
bistetrazole salts structurally characterised so far and correlat-
ing those to the coordination mode and potential chelating an-
gle an almost fully consecutive picture forms. Within the rare
earth metal salts a chelating coordination is observed for La,
Ce, Nd, Sm and Eu.[7a] The ionic radii for the respective coor-
dination number range from 1.26 Å (Eu3+, CN9) to 1.36 Å
(La3+, CN9).[30] Among the alkaline earth metal salts only with
strontium (ionic radius 1.32 Å, CN6) a chelating coordination bond lengths in the tetrazole moieties are consistent with the
is observed. Whereas the small cations Li+ (0.73 Å, CN4) and previous structures.
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Table 3. Comparison of ionic radii and coordination modes in known 5,5Ј-bistetrazole salts, ions ordered according to ionic radius.
Ion (CN)[a]
Be2+ (4) Li+ (4)
Mg2+ (6)
Cu2+ (6) Ca2+ (6) Er3+ (8) Na+ (6) Tb3+ (8) Th4+ (9)
Eu3+ (9)
Ionic radius /Å[30]
Coord. mode
Chelating angle /° N–M–N
Ion (CN)
0.41
none
0.73
single
0.86
none
0.87
chelate
72.7
1.14
single
1.14
none
1.16
single
1.18
none
1.23
none
1.26
chelate
62.9
Sm3+ (9) Nd3+ (9) Sr2+ (6)
Ce3+ (9) La3+ (9) Ba2+ (9) K+ (8)
Rb+ (8) Cs+ (8)
Ionic radius /Å
Coord. mode
Chelating angle /° N–M–N
1.27
chelate
62.7
1.30
chelate
62.2
1.32
chelate
64.1, 62.8 61.2
1.34
chelate
1.36
chelate
60.8
1.61
single
1.65
chelate chelate
57.2 55.6
1.75
1.88
chelate
53.6, 53.9
[a] Original literature: For Be, Mg, Ca, Sr and Ba see Ref. [8], for Cu see Ref. [9], for Er, Tb, Eu, Sm, Nd, Ce and La see Ref. [7a], for Th
see Ref. [7b], Li, Na, K, Rb and Cs are part of this work.
Figure 16. Molecular structure of ammonium 5,5Ј-bistetrazolate (9);
selected bond lengths /Å: C1–C1I: 1.463(4), C1–N1: 1.329(3), N1–
N2: 1.358(3), N2–N3: 1.310(3), N3–N4: 1.347(3), C1–N4: 1.327(3),
Figure 14. Molecular unit of diammonium 5,5Ј-bistetrazolate (8); se-
C2–C2II: 1.453(4), C2–N5: 1.337(3), N5–N6: 1.337(3), N6–N7:
lected bond lengths /Å and angles /°: C1–C1I: 1.461(3), C1–N1:
1.318(3), N7–N8: 1.334(3), C2–N8: 1.345(3); symmetry operations:
1.337(1), N1–N2: 1.345(1), N2–N2II: 1.318(2), N3···N1: 2.949(1),
I:–x, 1–y, 1–z, II: –x, –y, 1–z.
N3III···N2: 2.938(1), N1–C1–C1I–N1IV: 35.55(5), symmetry opera-
I
tions: : 1.5–x, 0.5–x, z; II: x, 0.5–y, –z; III: 1–x, 1–y, 1–z; IV: 1,5–x,
y, –z.
Figure 17. Crystal structure of monoammonium 5,5Ј-bistetrazolate (9);
view along the a axis; chains of BT monoanions connected over H-
bonds; only one position of the disordered hydrogen atom is displayed.
Figure 15. Crystal structure of diammonium 5,5Ј-bistetrazolate; a) hy-
drogen bonding; view in c direction; b) layered structure; view along
the b axis.
The structure is analogous to the structure of the caesium
5,5’-bitetrazolate (6). The positions of the caesium atoms are
As in the structure of CsHBT (6) the chains of bistetrazolate
occupied by ammonium ions. The bistetrazole moieties build anions are stacked and shifted with respect to each other so
hydrogen bonded chains (N4···N6: 2.679(3) Å), between which that every fifth layer is analogous. The stacks are tilted in a
the ammonium ions form a comparatively weaker hydrogen perpendicular fashion with respect to each other which be-
bonding network (donor acceptor distances between comes evident when the structure is viewed along the [210]
3.037(3) Å (N9···N8) and 3.065(3) Å (N9···N7), Figure 17).
direction (Figure 18).
8
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5,5’-Bistetrazolate Salts with Alkali Metal, Ammonium and Imidazolium Cations
Figure 18. Stacked layer structure of ammonium 5,5Ј-bistetrazolate,
neighboured stacks are tilted against each other by 90°; viewing direc-
tion [210]; only one position of the disordered hydrogen atom is dis-
Figure 20. Crystal structure of (EMIM)HBT (10); view along the
a axis.
played.
(EMIM)HBT (10) crystallised in the space group P21/n with
four molecules per unit cell (Figure 19). The bond lengths in
the bistetrazolate anion correspond well to the previous struc-
tures the imidazolium cation shows almost identical values,
when compared to common compounds.[31]
Figure 21. Molecular structure of Bis(1-ethyl-3-methylimidazolium)
5,5Ј-bistetrazolate; hydrogen atoms are omitted for clarity; selected
bond lengths /Å: C1–C1I: 1.460(2), C1–N1: 1.345(2), N1–N2:
1.354(2), N2–N3: 1.320(2), N3–N4: 1.355(2), C1–N4: 1.336(2), C2–
N5: 1.330(2), C2–N6: 1.327(2), C3–N6: 1.378(2), C3–C4: 1.350(2),
I
C4–N5: 1.385(2); symmetry operation: : –x, –y, –z.
Figure 19. Molecular structure of (EMIM)HBT (10); carbon bound
hydrogen atoms are omitted for clarity; selected bond lengths /Å: C1–
C2:1.454(2), C1–N1: 1.334(2), N1–N2: 1.354(2), N2–N3: 1.315(2),
N3–N4: 1.353(2), C1–N4: 1.335(2), C2–N5:1.324(2), N5–N6:
1.366(2), N6–N7: 1.299(2), N7–N8: 1.349(2), C2–N8: 1.334(2), C3–
N9: 1.329(2), C3–N10: 1.329(2), C4–N10: 1.373(2), C4–C5: 1.350(2),
C5–N9: 1.386(2).
In this case the monoanion of the 5,5’-bistetrazolate does
not form hydrogen-bonded chains as in compounds (6) and (9)
but hydrogen-bonded dimers (N8···N4: 2769(2) Å]. The dimers
are stacked in a direction and separated from neighbouring
stacks by imidazolium cations (Figure 20).
Bis(1-ethyl-3-methylimidazolium)
5,5’-bistetrazolate
Figure 22. Crystal structure of bis(1-ethyl-3-methylimidazolium) 5,5Ј-
bistetrazolate; view along the a axis; hydrogen atoms are omitted for
clarity.
((EMIM)2BT, 11) crystallised in the monoclinic space group
P21/n with two molecules in the unit cell; the asymmetric unit
consists of half a molecule (Figure 21). All bond lengths corre-
spond well to previous structures. The bistetrazolate dianion
being isolated from any further bonding contacts does not alter
its conformation. In the crystal structure stacks of molecular
units prevail when viewing along the a axis (Figure 22).
Thermal Analysis
Combined TGA and DSC measurements were conducted
with a Netzsch STA 409 CD under inert gas conditions (Ar,
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40 mL·min–1) in aluminium oxide crucibles with a hole in the drated and dehydrated salts. The hydrated salts show strong
lid. The applied heating rate was 10 K·min–1. Probe masses and broad stretching modes of the OH bonds involved in hy-
were in the range of 5.5 to 6.8 mg. The lithium salt (1h) loses drogen bonds roughly between 2500 and 3700 cm–1 and below
two equivalents of crystal water at 165 °C, the sodium salt (2h) 900 cm–1 the corresponding bending modes. The latter are
is dehydrated at 63 °C but the amount differs distinctively from often partly obscuring the vibrations of the BT fragment. The
the values observed in the crystal structure and the elemental water-free substances show a very concise spectrum built up
analysis. Instead of a weight loss of 33.1% corresponding to of seven major bands all lying within the fingerprint region
the pentahydrate, only a loss of 13.5% was observed. This at about 700 to 1400 cm–1. All bands slowly shift to lower
indicates a crystal water content of one to two equivalents. It wavenumbers when proceeding from lithium to caesium as
is assumed, that water was lost during storage and while evac- counterion. A distinct effect of the atomic weight of the coun-
uating the oven in order to ensure an inert gas atmosphere. terion onto the lattice vibrations of the BT-fragment can be
Among the alkali metal salts only the caesium salt (5) decom- observed. A comparison of the region from 680 to 1400 cm–1
poses below 400 °C (392 °C). The other salts show decomposi- of the water-free alkali metal salts of 5,5’-bistetrazole are pre-
tion at onset temperatures of 416 (Rb2BT), 424 (K2BT), 453 sented in Figure 23. The barium salt roughly fits into this trend
(Na2BT) and 478 °C (Li2BT). These values coincide with the taking into account that the atomic weight of the barium atom
observations of Klapötke et al. who found no decomposition has to be considered with 50% as only one barium atom is
of the alkaline earth metal salts below 400 °C.[8] In all cases present per BT moiety.
the decomposition is not complete at the stated temperatures
but only a fraction of the total mass is lost. Upon continued
heating the residues decompose in a stepwise manner but
rather gradually so that no further definite decomposition tem-
peratures can be determined. Thermal decomposition is com-
plete at close to 1000 °C. The monoammonium salt (9) shows
decomposition at an onset temperature of 282 °C, the diammo-
nium salt (8) measured for direct comparison showed decom-
position at 290 °C. This value corresponds well to the tempera-
ture observed by Chavez et al. (280 °C, the difference may be
due to a higher heating rate in our case).[29] The monoammo-
nium and the diammonium salt show no large difference con-
cerning thermal behaviour. If there is a specific and consider-
able advantage of the monoammonium 5,5’-bistetrazolate over
the diammonium salt it has to affect different properties. The
DSC curve of (EMIM)HBT (10) shows an endothermic peak
at 147 °C, which is not accompanied by a weight loss in the
TGA curve and can therefore be attributed to the substance
melting. Decomposition takes place at 266 °C. (EMIM)2BT
even melts at just 95 °C and can therefore be classified as an
ionic liquid. The decomposition of the substance follows at
Figure 23. Comparison of the IR spectra of the water-free alkali metal
5,5Ј-bistetrazolates in the region from 680 to 1400 cm–1.
Conclusions
250 °C. The melting points were redetermined with a slower
heating rate (2 K·min–1) rate with a Büchi Melting Point B540.
The melting point of 10 was determined as 145.5 °C,
(EMIM)2BT (11) melted at 92.5 °C. The melting points stayed
unchanged over three temperature cycles between room tem-
perature and 10 °C above the melting point. To the best of our
knowledge these are the first bistetrazolate salts exhibiting a
distinct melting point. Compound 11 is a rare example of an
ionic liquid containing a dianion, nevertheless having low lat-
tice energy. The TGA of 11 reveals an abrupt loss of 80%
weight at an onset of 249.6 °C in connection with an exother-
mic peak in the DSC (see electronic supplement). Only small
amounts of substance remain after the first decomposition.
The alkali metal salts 1 to 5 of the nitrogen-rich diacid 5,5’-
bistetrazole were synthesised and characterised by elemental
analysis, carbon NMR and IR spectroscopy and TGA and DSC
measurements. The corresponding hydrates 1h to 4h and the
mono caesium 5,5’-bistetrazolate (6) were structurally charac-
terised by means of XRD single crystal analyses. Additionally,
a second crystal modification of the known barium 5,5’-biste-
trazolate (7h) was presented. The compounds have been ana-
lysed with respect to the coordination behaviour of the bicyclic
ligand and the results compared with all metal 5,5’-bistetrazol-
ates structurally characterised so far. A consecutive trend be-
tween chelation and the cation size was found and attributed
to the Lewis acidity of the cation and the geometric limitations
of the rather rigid ligand. Furthermore the monoammonium
5,5’-bistetrazolate (9), and mono- (10) and bis(1-ethyl-3-meth-
IR Spectroscopy
IR spectra were recorded with a Bruker ALPHA FT IR spec- ylimidazolium) 5,5’-bistetrazolate (11) were synthesised and
trometer with platinum ATR sampling as the pure substance. fully characterised including single crystal structure determi-
There is a strong difference between the spectra of the hy- nation. The diammonium 5,5’-bistetrazolate (8) is additionally
10
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5,5’-Bistetrazolate Salts with Alkali Metal, Ammonium and Imidazolium Cations
(ATR): 417 (s), 742 (w), 1040 (w), 1064 (w), 1168 (w), 1209 (w),
presented in a different crystal modification as it was known
so far. No special properties could be attributed to the
monoammonium salt 9, to be used in airbag technology, setting
it apart from the diammonium salt (8), so far. The imidazolium
salts are the first reversibly melting 5,5’-bistetrazolate com-
pounds, the bis(1-ethyl-3-methylimidazolium) 5,5’-bistetrazo-
late (11) being the first ionic liquid on the basis of 5,5’-bis-
tetrazolate dianions.
1324 (w), 1346 (w) cm–1.
Disodium 5,5’-bistetrazolate pentahydrate (2h): Sodium hydrogen
carbonate (1.38 g, 16.5 mmol) and 5,5’-bistetrazole (1.14 g,
8.24 mmol) were suspended in water (5 mL). The solids dissolved
slowly accompanied by gas evolution. After the gas evolution had
stopped, the mixture was heated to obtain a clear solution. The solvent
was evaporated to dryness and the residue recrystallised from a mini-
mum amount of hot water (ca. 3 mL) obtaining single crystals suitable
for XRD. The sodium salt crystallised as a pentahydrate in 60% yield
(1.35 g, 4.96 mmol).
Experimental Section
C2H10N8Na2O5 (272.13 g·mol–1) C 8.73 (calcd. 8.83), H 3.38 (3.70),
N 41.11 (41.18)%; 13C NMR (75.5 MHz, D2O): δ = 154.5 (s, CN4)
ppm. IR (ATR): 499 (m, sh), 579 (s, br), 730 (m), 1022 (m), 1047
(w), 1148 (m), 1186 (m), 1307 (s), 1326 (s), 1628 (s), 2600–3600 (s,
br) cm–1; TGA (10 K·min–1): 63 (dehydr.), 453 (decomp.) °C; DSC
(10 K·min–1): 85 (endoth.), 464 (exoth.) °C.
All chemicals and solvents were used as received unless stated other-
wise. Methanol, acetonitrile and diethyl ether were dried and purified
according to common procedures[32] and stored over 3 Å molecular
sieves until use. Elemental analyses were carried out by the service
department for routine analysis and mass spectrometry with a vario
MICRO cube (Elementar). NMR spectra were recorded in automation
with a Bruker Avance 300 spectrometer at room temperature. IR spec-
tra were recorded with a Bruker APLPHA FT-IR spectrometer with
Platinum ATR-sampling. Hygroscopic substances were investigated on
an identical device inside a glove box (type MB 150 B-G, mBraun).
TGA/DSC measurements were performed with a Netzsch STA 409 CD
in aluminium oxide crucibles, with an argon flow rate of
40 mL·min–1 and a heating rate of 10 K· min–1; TGA decomposition
points are given as onset temperature, DSC data is given as peak value.
Melting points were determined with a Büchi Melting Point B540.
Drying in fine vacuum at 90 °C yielded the water-free disodium salt
(2).
C2N8Na2 (182.06) C 12.99 (calcd. 13.19), N 60.52 (61.55)%. IR
(ATR): 734 (s), 1015 (s), 1049 (m), 1148 (m), 1182 (m), 1308 (s),
1345 (s) cm–1.
Dipotassium 5,5’-bistetrazolate (3): Potassium carbonate (1.65 g,
12.0 mmol) and 5,5’-bistetrazole (1.50 g, 10.9 mmol) were suspended
in water (15 mL) and after the gas evolution had ceased the mixture
was heated to reflux. The solvent was evaporated at room temperature
and the residue recrystallised from boiling water (4.5 mL). Single crys-
tals suitable for XRD were obtained but did not lead to publishable
solutions. In one case the investigated crystal turned out to be the
corresponding dihydrate 3h. The product was dried in air at room tem-
perature yielding 1.42 g (6.63 mmol, 61%).
Caution! 5,5’-Bistetrazole and its derivatives are potential explosives
and sensitive to heat, shock, friction and electrical spark. Although
no unintended decomposition was observed during our experiments
cautious handling of all substances and protective gear like safety
shields, gloves, earthed equipment and earplugs are strongly recom-
mended. Furthermore the handling and storage of larger quantities
should be avoided.
C2K2N8 (214.27 g·mol–1) C 11.14 (calcd. 11.21), N 52.42 (52.30)%;
13C NMR (75.5 MHz, D2O): δ = 154.7 (s, CN4) ppm. IR (ATR): 732
(s), 1009 (s), 1042 (m), 1140 (m), 1170 (m), 1302 (s), 1334 (s) cm–1;
TGA (10 K·min–1): 424 (decomp.) °C; DSC (10 K·min–1): 429 (ex-
oth.) °C.
5,5’-Bistetrazole was prepared following the procedure invented by
Friederich[3] and optimised by Nelson et al.[4] Diammonium 5,5’-biste-
trazolate (8) was synthesised according to Hyoda et al.[33] and later on
in a way also described by Klapötke et al.[10a] Analysis for compound
8: TGA (10 K·min–1): 290 °C (decomp.); DSC (10 K·min–1): 305 °C
(exoth.)
Dirubidium 5,5’-bistetrazolate dihydrate (4h): Rubidium carbonate
(1.32 g, 5.72 mmol) was suspended in water (15 mL) and 5,5’-bistetra-
zole (790 mg, 5.72 mmol) was added. After the gas evolution had
ceased the water was evaporated on a hot plate and the slightly yellow
residue recrystallised from a minimum amount of water (3 mL). Single
crystals suitable for XRD could be obtained. The X-ray structure in-
cludes two water molecules per molecular unit which are lost while
drying in air at room temperature. During the drying process the crys-
tals transform from colourless translucent needles to a colourless pow-
Dilithium 5,5’-bistetrazolate dihydrate (1h): Lithium hydroxide
monohydrate (301 mg, 7.18 mmol) and 5,5’-bistetrazole (496 mg,
3.59 mmol) were suspended in water (5 mL) and the mixture heated
to reflux. The clear hot solution was filtered and the solvents evapo-
rated to dryness. The raw product (654 mg, 3.52 mmol, 98%) was
recrystallised from a minimum amount of water yielding 48%
(319 mg) of 1h and crystals suitable for XRD.
C2H4Li2N8O2 (185.99 g·mol–1) C 12.80 (calcd. 12.92), H 2.05 (2.17), der. Water-free rubidium 5,5’-bistetrazolate (4) was obtained in 62%
N 59.80 (60.25)%; 13C NMR (75.5 MHz, [D6]DMSO): δ = 155.4 (s,
CN4) ppm; 13C NMR (75.5 MHz, D2O): δ = 154.5 (s, CN4) ppm. IR
(1034 (m), 1066 (w), 1169 (w), 1212 (m), 1317 (w), 1345 (m),
2600–3400 (m, br) cm–1; TGA (10 K·min–1): 165 (dehydr.), 478 (de-
comp.) °C; DSC (10 K·min–1): 182 (endoth.), 479 (exoth.) °C.
yield (1.10 g).
C2Rb2N8 (307.02 g·mol–1) C 7.75 (calcd. 7.82), N 36.36 (36.50)%; 13
NMR (75.5 MHz, D2O): δ = 154.7 (s, CN4) ppm. IR (ATR): 733 (m),
1009 (s), 1040 (m), 1136 (m), 1169 (m), 1296 (s), 1325 (s) cm–1; TGA
(10 K·min–1): 416 (decomp.) °C; DSC (10 K·min–1): 424 (exoth.) °C.
C
Drying the product at 180 °C in fine vacuum yielded the water-free
salt (1). The substance is highly hygroscopic and upon air contact ab-
sorbs two equivalents of water within minutes.
Dicaesium 5,5’-bistetrazolate (5): Caesium carbonate (2.16 g,
8.96 mmol) and 5,5’-bistetrazole (760 mg, 5.50 mmol) were dissolved
in water (15 mL) and the solution was evaporated to dryness after
stirring for 30 minutes. The residue was recrystallised from a small
amount of hot water and the product was isolated in 70% yield (1.55 g,
C2Li2N8 (149.96 g·mol–1) C 15.72 (calcd. 16.02), N 74.63 (74.72)%;
13C NMR (75.5 MHz, [D6]DMSO): δ = 155.6 (s, CN4) ppm. IR
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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L. H. Finger, F. G. Schröder, J. Sundermeyer
ARTICLE
3.86 mmol). Single crystals could be obtained but did not lead to a
publishable solution so far.
3-methylimidazolium bisulfate (356 mg, 1.71 mmol) in water (20 mL).
The suspension was stirred for three days and then filtered. The solu-
tion was evaporated to dryness and the residue recrystallised from a
hot mixture of acetone and water. Single crystals suitable for XRD
were obtained by layering a concentrated solution in acetonitrile with
diethyl ether. Yield: 220 mg (0.87 mmol, 52%).
C2Cs2N8 (401.90 g·mol–1) C 6.09 (calcd. 5.89), N 27.92 (27.88); 13C
NMR (75.5 MHz, D2O): δ = 154.6 (s, CN4) ppm. IR (ATR): 733 (m),
1006 (s), 1035 (m), 1111 (w), 1120 (w), 1130 (m), 1169 (m), 1290 (s),
1314 (s) cm–1; TGA (10 K·min–1): 392 (decomp.) °C; DSC
(10 K·min–1): 402 (exoth.) °C.
C8H12N10 (248.25 g·mol–1) C 38.48 (calcd. 38.71), H 4.80 (4.87), N
55.60 (56.42)%; 1H NMR (300.1 MHz, [D6]DMSO): δ = 1.40 (t, 3 H,
3J(H,H) = 7.2 Hz, CH2CH3), 3.85 (s, 3 H, Me), 4.19 (q, 3JH,H = 7.2 Hz,
2 H, CH2CH3), 7.70 (s, 1 H, HIm), 7.78 (s, 1 H, HIm), 9.15 (s, 1 H,
HIm), 16.19 (br. s, 1 H, HBT) ppm; 13C NMR (75.5 MHz, [D6]DMSO):
δ = 15.0 (s, CH2CH3), 35.7 (s, CH3), 44.1 (s, CH2CH3), 121.9 (s, CIm),
123.5 (s, CIm), 136.3 (s, CIm), 149.4 (s, CN4) ppm. IR (ATR): 412 (w),
483 (s), 627 (s), 650 (s), 703 (m), 758 (s), 866 (m), 890 (m), 999 (m),
1017 (m), 1029 (m), 1092 (m), 1161 (s), 1281 (m), 1341 (s), 1465 (w),
1560 (w), 1574 (w), 1617 (w), 2300–2700 (w, br), 3112 (w), 3141 (w)
cm–1; TGA (10 K·min–1): 266 (decomp.) °C; DSC (10 K·min–1): 147
(endoth.), 282 (exoth.) °C; M. P. (2 K·min–1): 145.5 °C.
Barium 5,5’-bistetrazolate pentahydrate (7h): Barium hydroxide
octahydrate (3.88 g, 12.3 mmol) and 5,5Ј-bistetrazole (1.70 g,
12.3 mmol) were dissolved in boiling water (100 mL). The solution
was filtered hot and slowly cooled to room temperature. The product
crystallised in 79% yield (3.55 g, 9.77 mmol), single crystals suitable
for XRD analysis could be obtained.
Pentahydrate: C2H10BaN8O5 (363.49 g·mol–1) C 6.61 (calcd. 6.61), H
2.20 (2.77); N 31.00 (30.83)%; 13C NMR (75.5 MHz, D2O): δ = 155.4
(s, CN4) ppm. IR (ATR): 400–850 (s, br), 1021 (s), 1048 (m), 1121
(w), 1151 (m), 1181 (s), 1308 (s), 1327 (s), 1650 (m), 2700–3600 (s,
br) cm–1. The comparatively high deviation of the hydrogen value may
indicate a partial mixture of e.g. the penta- and tetrahydrate. This is
not confirmed by the nitrogen value, though. Drying the Substance in
air at room temperature yielded the dihydrate after four days.
Bis(1-ethyl-3-methylimidazolium) 5,5’-bistetrazolate (11): A solu-
tion of 5,5’-bistetrazole (349 mg, 2.53 mmol) in dry methanol (10 mL)
was slowly added to a solution of 1-Ethyl-3-methylimidazolium
methyl carbonate (938 mg, 5.04 mmol) in dry methanol (5 mL). Slow
gas evolution was observed and the mixture was heated to 50 °C for
sixteen hours before the solvent was removed in vacuo. The residue
was recrystallised by layering a concentrated solution in dry acetoni-
trile with dry diethyl ether. Large crystals suitable for XRD formed
within hours, crystallisation was complete after a few days. After a
second recrystallisation from dry acetonitrile at –30 °C 560 mg
(1.56 mmol, 62%) of the pure product were obtained.
Dihydrate: C2H4BaN8O2 (309.45 g·mol–1) C 7.70 (calcd. 7.76), H 1.26
(1.30), N 35.94 (36.21)%. IR (ATR): 542 (s, br), 571 (s, sh), 675 (m,
br), 725 (m), 819 (w, br), 1019 (m), 1047 (w), 1085 (w), 1143 (w),
1186 (w), 1218 (w), 1310 (m), 1339 (m), 3057 (w, br) 3523 (w, br)
cm–1.
Drying the product at 120 °C in fine vacuum for four hours yielded
the water-free salt.
C14H22N12 (358.41 g·mol–1) C 47.10 (calcd. 46.92), H 6.21 (6.19), N
46.91 (46.90)%; 1H NMR (300.1 MHz, [D6]DMSO): δ = 1.37 (t, 3 H,
C2BaN8 (273.42 g·mol–1) C 8.79 (calcd. 8.79), N 41.54 (40.98)%. IR
(ATR): 728 (m), 1021 (s), 1057 (m), 1085 (w), 1143 (s), 1191 (m),
1312 (m), 1340 (s) cm–1.
3
3JH,H = 7.1 Hz, CH2CH3), 3.89 (s, 3 H, Me), 4.25 (q, JH,H = 7.1 Hz,
2 H, CH2CH3), 7.76 (s, 1 H, HIm), 7.85 (s, 1 H, HIm), 9.67 (s, 1 H,
HIm) ppm; 13C NMR (75.5 MHz, [D6]DMSO): δ = 15.2 (s, CH2CH3),
35.5 (s, CH3), 44.0 (s, CH2CH3), 121.9 (s, CIm), 123.5 (s, CIm), 136.8
(s, CIm), 156.0 (s, CN4) ppm. IR (ATR): 621 (m), 651 (s), 732 (s), 739
(s), 800 (m), 850 (w), 894 (m), 1006 (w), 1027 (m), 1094 (w), 1156
(s), 1293 (m), 1315 (m), 1428 (w), 1453 (w), 1561 (m), 1659 (w),
2978 (w), 3053 (m), 3136 (w) cm–1 TGA (10 K·min–1): 250 (decomp.)
°C; DSC (10 K·min–1): 94.5 (endoth.), 298 (exoth.) °C; M. P.
(2 K·min–1): 92.5 °C.
Ammonium 5,5’-bistetrazolate (9): Diammonium 5,5’-bistetrazolate
(554 mg, 3.22 mmol) and 5,5’-bistetrazole (445 mg, 3.22 mmol) were
dissolved in water (25 mL), the solution heated to reflux and then
evaporated to dryness. The residue was recrystallised from a minimum
amount of hot water (ca. 5 mL) so that an aqueous solution at 115 °C
in a closed flask was saturated. The solution was then slowly cooled to
room temperature yielding needles of diammonium 5,5’-bistetrazolate
(201 mg, 1.17 mmol, 36% of the starting material. C2H8N10
(172.15 g·mol–1) C 13.86 (calcd. 13.95), H 4.55 (4.68), N 80.98
(81.36)%). The supernatant solution was transferred to a second flask
and slowly cooled to 4 °C whereupon the desired product crystallised
in 60% yield (302 mg, 1.95 mmol). Single crystals suitable for XRD
were obtained.
Supporting Information (see footnote on the first page of this article):
Table with bond lengths, bond angles and torsion angles in the bistetra-
zolate anions of compounds, 1h to 4h, 6, 7h and 8 to 11; TGA and
DSC Curve of (EMIM)2BT (11).
C2H5N9 (155.12 g·mol–1) C 15.65 (calcd. 15.49); H 2.92 (3.25), N
80.64 (81.27)%; 13C NMR (75.5 MHz, D2O): 149.4 (s, CN4) ppm. IR
(ATR): 426 (m), 476 (s), 687 (m), 851 (s, br), 1009 (s), 1070 (m),
1105 (m), 1224 (w), 1282 (m), 1335 (w), 1377(s), 1409 (m), 1528
(w), 2100–3300 (m, br); TGA (10 K·min–1): 282 (decomp.) °C; DSC
(10 K·min–1): 289 (exoth.) °C. The deviation of the nitrogen value
in the elemental analysis may be attributed to the product not being
completely pure. The tendency of equimolecular solutions of diammo-
nium 5,5’-bistetrazole and the free acid to yield the diammonium salt
upon crystallisation makes it not possible to purify the product by
recrystallisation.
Acknowledgments
Financial support by the Studienstiftung des deutschen Volkes and the
Fond der Chemischen Industrie is gratefully acknowledged. We thank
Jens Eußner (M. Sc.) for his introduction into and continued help with
TGA/ DSC measurements. We are very thankful to Dr. Klaus Harms
for fruitful discussions and valuable advice regarding XRD single crys-
tal structure determination.
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12
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5,5’-Bistetrazolate Salts with Alkali Metal, Ammonium and Imidazolium Cations
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Received: March 12, 2013
Published Online: ᭿
Z. Anorg. Allg. Chem. 0000, 0–0
© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Date: 21-05-13 16:49:20
Pages: 14
L. H. Finger, F. G. Schröder, J. Sundermeyer
ARTICLE
L. H. Finger, F. G. Schröder, J. Sundermeyer* .............. 1–14
Synthesis and Characterisation of 5,5’-Bistetrazolate Salts with
Alkali Metal, Ammonium and Imidazolium Cations
14
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