Crystal structures of the potassium and silver salts of nitroform

Article abstract of DOI:10.1002/zaac.200500525

The solid state structures of three nitroformate (NF) salts were determined using single crystal X-ray crystallography. The NF anion was found to be a non-planar moiety which adopts either the commonly observed C_2v conformation or distorted propeller conformation (D₃) in the case of the silver salts, or, a C₂ conformation in the case of the potassium salt. This latter C₂ conformation has been uniquely observed for potassium nitroformate. All structures exhibit cation-anion interactions that influence the structure of the anion. The ¹³C and ¹⁴N NMR spectra of the NF anion show broad singlets, which indicates the equivalence of the nitro groups in solution within the NMR time-scale. In addition, the vibrational and mass spectra of potassium nitroformate and silver nitroformate monohydrate were recorded. Furthermore, the gaseous decomposition products of potassium nitroformate at 25 °C were detected using IR spectroscopy and mass spectrometry.

Full text of DOI:10.1002/zaac.200500525

DOI: 10.1002/zaac.200500525
Crystal Structures of the Potassium and Silver Salts of Nitroform
Michael Göbel, Thomas M. Klapötke*, and Peter Mayer
Munich / Germany, Ludwig-Maximilian University, Department of Chemistry and Biochemistry
Received December 23rd, 2005.
Dedicated to Professor Hansgeorg Schnöckel on the Occasion of his 65th Birthday
Abstract. The solid state structures of three nitroformate (NF) salts
were determined using single crystal X-ray crystallography. The NF
anion was found to be a non-planar moiety which adopts either
the commonly observed C2v conformation or distorted propeller
conformation (D3) in the case of the silver salts, or, a C2 conforma-
tion in the case of the potassium salt. This latter C2 conformation
has been uniquely observed for potassium nitroformate. All struc-
tures exhibit cation-anion interactions that influence the structure
of the anion. The 13C and 14N NMR spectra of the NF anion show
broad singlets, which indicates the equivalence of the nitro groups
in solution within the NMR time-scale. In addition, the vibrational
and mass spectra of potassium nitroformate and silver nitroformate
monohydrate were recorded. Furthermore, the gaseous decomposi-
tion products of potassium nitroformate at 25 °C were detected
using IR spectroscopy and mass spectrometry.
Keywords: Silver nitroformate; Potassium nitroformate; Crystal
structures; NMR spectroscopy; Energetic salts
Introduction
NMR spectra of the anion in the potassium and silver salts
both showed one signal at room temperature. The signals
of the potassium salt could be observed at 150.8 ppm (13C)
and -30.3 ppm (14N) and for the silver salt at 150.4 ppm
(13C) and Ϫ29.9 ppm (14N) in DMSO-d6. These values fit
well with those reported by Gakh et al. [5], who reported
the 13C chemical shifts of the cesium and the tetrabutyl-
ammonium salts of the nitroformate anion at 150.3 ppm
and 151.6 ppm (both recorded in acetone-d6), respectively.
The reported line broadening in the 13C spectra due to
13CϪ14N spin interactions which are known for such
systems [6, 7] was confirmed by our results. Both the
potassium and the silver salts of nitroform are bright-yellow
solids, which can be explained by a n-π* transition at a
wavelength of 350 nm. There is a further π-π* transition in
the UV region which is however not visible [8]. The thermal
behavior of the salts has been investigated using a differen-
tial scanning calorimeter (Perkin-Elmer Pyris 6 DSC) at
heating rates of 5 °C minϪ1 (Figure 1).
Nitroform, CH(NO2)3, holds a special position among nitro
compounds as it participates in many reaction types, includ-
ing replacement, condensation and nitration reactions. A
number of reactions which involve the nitroformate anion
utilize the potassium or the silver salt. Although the prep-
aration of both of these salts has been described previously
[1], to the best of our knowledge, the single crystal struc-
tures, NMR spectra as well as the vibrational- and mass
spectra of the silver salts as well as of this modification of
potassium nitroformate were not reported. In this investi-
gation, the synthesis of the compounds was repeated ac-
cording to the reported literature procedures [2, 3] and the
compounds were characterized using various methods for
the first time. In addition, the gaseous decomposition prod-
ucts of potassium nitroformate formed on standing at room
temperature were identified using IR spectroscopy as well
as mass spectrometry. In addition to those cited previously
in the literature [4], two further decomposition products
were observed.
The onset temperatures of the decomposition of silver
nitroformate monohydrate and potassium nitroformate
were found to be 65 °C (AgNFH) as well as 80 °C (KNF).
In the case of the silver nitroformate monohydrate one exo-
thermic peak could be observed whereas in the case of the
potassium nitroformate three exothermic peaks were re-
corded.
Results and Discussion
An investigation of the NF anion in solution was performed
using 13C and 14N NMR spectroscopy. The 13C and 14N
Potassium nitroformate was obtained according to the re-
ported literature procedure from the reaction of tetranitro-
methane with potassium hydroxide and glycerol in water
solution [2].
* Prof. Dr. Thomas M. Klapötke
Department of Chemistry and Biochemistry
Ludwig-Maximilan University
Butenandtstr. 5-13 (Haus D)
D-81377 Munich / Germany
E-mail: tmk@cup.uni-muenchen.de
C(NO2)4 ϩ KOH ϩ C3H8O3 Ǟ KC(NO2)3 ϩ
H2O ϩ C3H7NO4 (1)
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M. Göbel, T. M. Klapötke, P. Mayer
Figure 2 IR spectrum of the gaseous decomposition products of
KC(NO2)3 recorded after a decomposition time of one day at
room temperature.
N2O: 3492(m), 3463(m), 3376(w), 3351(w), 2797(w), 2576(m), 2553(m),
2474(w), 2447(w), 2237(vs), 2213(vs), 1697(w), 1301(s), 1273(s), 1180(w),
1152(w), 589 (m); NO: 1879 (w); CO: 2197(vs), 2188(vs); CO2: 3851(w),
3822(w), 3737(w), 3711(w), 2335(vs), 668(s) cmϪ1
.
Figure 1 Thermal behavior of KC(NO2)3 (KNF) as well as
AgC(NO2)3·H2O (AgNFH) at heating rates of 5 °C minϪ1 recorded
using a differential scanning calorimeter.
Golovina et al. reported two different crystal shapes of
potassium nitroformate when recrystallizing the salt from
water [9]. They observed both needle-like crystals as well
as rhombohedral crystals. However, the latter crystals were
reported to be highly reactive and too unstable to be meas-
ured. We have now managed to selectively obtain octa-
hedral shaped crystals by recrystallizing potassium nitrofor-
mate from nitromethane. In order to protect the crystals
from decomposition, they were immediately placed under
and maintained in perfluorinated oil at 0 °C prior to meas-
uring. Figure 1 of the supplementary material shows both
a photograph of these crystals and the decomposition of
the crystals with the evolution of gas. The gaseous de-
composition products that formed when KC(NO2)3 was left
in vacuum (1Ⴇ10Ϫ3 mbar) at room temperature for a period
of four days were detected using IR spectroscopy (Figure
2) as well as high resolution mass spectrometry (Figures
3Ϫ5) and were found to be CO2, N2 and NO as cited pre-
viously in the literature [4] and, in addition, N2O and CO
using IR spectroscopy (Figure 2) as well as high resolution
mass spectrometry (Figures 3Ϫ5).
Figure 3 Mass spectrum of the gaseous decomposition products
of KC(NO2)3. The spectrum was measured using the EIϩ ion
mode.
of the NF anion in the gas phase seems to be one with two
in-plane nitro groups (dihedral angles close to 0°) and the
third nitro group twisted out of the C-N3 plane (C2v like
structure). This conformer represents the global minimum
and is reported to be energetically favored by 0.5 kcal/mol
in comparison to the isomer with D3 symmetry, which ad-
opts a propeller-like structure with all three nitro groups
twisted more evenly with respect to the central plane [24].
In contrast, the NF anion in the potassium salt shows one
nitro group (N2 in Figure 6) that is nearly coplanar with
the C-N3 moiety with a torsional ONCN angle of 8.0°,
while the other two nitro groups are twisted with a torsional
ONCN angle of 33.8° resulting in an anion with C2 sym-
metry. A view along the b axis of the unit cell as well as a
view along the a axis of the unit cell reveals an interesting
structural motif. The NF anions form a wavelike band to-
The interplay of several factors that affect the structure
of the nitroformate anion is complex and has been the sub-
ject of several publications [10, 13, 14]. Existing data in-
clude the results of ab initio calculations [13, 14] and single
crystal X-ray crystallographic studies [15Ϫ3]. The potass-
ium salt crystallizes in the highly symmetric tetragonal
¯
space group I42d (no. 122) with eight formula units per
unit cell.
The anion shows the typical, planar C-N3 moiety, how-
ever, the conformation of the nitro groups is unique, and is
different to the structures that have been previously re-
ported in the literature. According to theoretical calcu-
lations [24], the energetically most favorable conformation
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Potassium and Silver Salts of Nitroform
Figure 6 Structure of the asymmetric unit of KC(NO2)3 in the
crystal. The thermal ellipsoids in are drawn with a probability fac-
tor of 50 %.
Figure 4 High resolution mass spectrum of the gaseous decompo-
sition products of KC(NO2)3. The spectrum was measured using
the EIϩ mode.
Figure 7 Unit cell of KC(NO2)3 along the b axis. The thermal
ellipsoids are drawn with a probability factor of 50 %.
veals the high symmetry of the space group with four two-
fold rotation axes, six ’Diamond’ glide planes, nine inver-
sion axes and ten two-fold screw axes (Figure 8).
For the discussion of the coordination of the potassium
˚
cation, a value of 3.6 A was chosen as a reasonable value
for electrostatic interaction in agreement with the literature
[25]. The potassium cation is surrounded by twelve oxygen
atoms which belong to seven nitroformate anions, resulting
in a bicapped pentagonal metaprism geometry to the pot-
assium cation. Five anions are coordinated in a wheel like
way around the potassium ion forming the edges of the pen-
tagonal metaprism. Each of these five anions is coordinated
to the potassium cation via two oxygen atoms. In two cases,
the two oxygen atoms belong to two different nitro groups
of one anion and in the other three, the two oxygen atoms
belong to the same nitro group of one anion. The metapr-
ism is capped by one anion coordinating to the potassium
cation with only one oxygen atom of one nitro group at
Figure 5 High resolution mass spectrum of the gaseous decompo-
sition products of KC(NO2)3. The spectrum was measured in the
EIϩ mode.
gether with the potassium cation along the c axis in both
cases (Figure 7).
The anions which do not participate in this wavelike pat-
tern in Figure 7 correspond to the same wavelike pattern
along the c axis when considering the unit cell along the a
axis and the other way round. A view along the c axis re-
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M. Göbel, T. M. Klapötke, P. Mayer
Figure 9 Structure of the asymmetric unit of AgC(NO2)3·H2O in
the crystal. The thermal ellipsoids are drawn with a probability
factor of 50 %, only the hydrogen atoms are drawn with a probabi-
lity factor of 10 % for clarity.
Figure 8 Unit cell of KC(NO2)3 along the c axis. The thermal
ellipsoids are drawn with a probability factor of 50 %.
˚
each side. The shortest potassium-oxygen distance (2.73 A)
is observed when the oxygen atoms belong to the nitro
group with a torsional angle of only 8.0°. This can be
understood in terms of the HSAB principle, whereby a
small torsional angle between the nitro group and the
C-N3 plane allows for better overlap of the π-orbitals of the
carbon and nitrogen atoms. This thereby allows the carbon
atom to donate its negative charge to the nitro group
towards the more electronegative oxygen atoms making
them harder and therefore, the most suitable oxygen atoms
of the anion to interact with the potassium cation.
Figure 10 Unit cell of AgC(NO2)3·H2O along the a axis. The ther-
mal ellipsoids are drawn with a probability factor of 50 %, only
the hydrogen atoms are drawn with a probability factor of 10 %
for clarity.
exposure of the crystals to light has to be strictly avoided
otherwise the crystals immediately become opaque.
The sensitivity data of potassium nitroformate were
measured in order to establish safe handling procedures for
this compound. Two different instruments were used to de-
termine the friction and impact sensitivity: the Bundesan-
stalt für Materialforschung und Prüfung (BAM) drop ham-
mer (BAM fh (Fallhammer)) and friction tester (BAM ft).
Potassium nitroformate was found to meet the United Na-
tions (UN) recommendations for the transport of danger-
ous goods, with a friction sensitivity of greater than 360 N
and an impact sensitivity of greater than 29.6 J. In contrast,
great care should be taken when handling silver nitrofor-
mate salts. Heavy metal salts of energetic anions are known
as primary explosives in priming compositions for bullets,
initiating compositions for blasting caps and detonators,
such as lead azide, lead styphnate and mercury fulminate.
Single crystals of silver nitroformate monohydrate were
obtained by recrystallizing silver nitroformate from water
and drying in the oven at 40 °C. It is a challenging task to
obtain single crystals of the compound, as crystal growth
has to compete with the decomposition of silver nitrofor-
mate, which occurs even at room temperature. In addition,
2 HC(NO2)3 ϩ Ag2O Ǟ 2 AgC(NO2)3 ϩ H2O
(2)
The structure of the silver salt is much more complex
than that of the potassium salt, whereby AgC(NO2)3·H2O
has two crystallographically different ion pairs in the asym-
metric unit. The salt crystallizes in the monoclinic space
group P21/n (no. 14) with eight formula units per unit cell.
The crystallographically imposed two-fold screw axes trans-
form the structural motives into each other.
Both nitroformate anions in AgC(NO2)3·H2O show a dis-
torted C2v conformation which is the most common for
nitroformate anions. The sum of the NCN angles are 359.8°
and 359.9° resulting in the expected planar C-N3 moiety. In
each anion, two of the nitro groups lie nearly in plane with
dihedral angles of 9.3°, 2.3° and 10.4°, 3.0° respectively. The
third nitro group is twisted out of the plane with a dihedral
angle of 39.9° for one anion and 46.2° for the other. Within
˚
a radius of 3.6 A, the first silver cation is surrounded by
eleven oxygen atoms belonging to one molecule of water
and six nitroformate anions. Out of these six nitroformate
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Potassium and Silver Salts of Nitroform
anions, two anions coordinate via only one oxygen atom of
one nitro group. Three further anions coordinate via both
oxygen atoms of one nitro group and one anion coordinates
two times with only one oxygen atom of one nitro group.
The second silver cation is surrounded by ten oxygen atoms
belonging to two water molecules and five nitroformate
anions. There are also three different possible coordination
modes. In one case, two anions coordinate via only one oxy-
gen atom of one nitro group. In another coordination
mode, two further anions coordinate to the silver cation
through both oxygen atoms of one nitro group and a final
possibility that was also observed is the coordination of one
anion twice with only one oxygen atom of a nitro group.
Recrystallization of silver nitroformate monohydrate
from acetic acid anhydride at room temperature yields
single crystals of silver nitroformate hemi hydrate
AgC(NO2)3·0.5 H2O. This compound is even more reactive
than the monohydrate. Single crystals of silver nitroformate
hemi hydrate decompose with the liberation of gas, as was
also observed for crystals of potassium nitroformate.
Whereas the potassium nitroformate crystals were stable
under perfluorinated oil at room temperature for several
minutes, single crystals of silver nitroformate hemi hydrate
decompose under perfluorinated oil even when being co-
oled to 0 °C. A photograph of these crystals can be found
in Figure 2 of the supplementary material. In order to
measure these crystals, they were maintained at liquid nitro-
gen temperature and selected under red light. Due to this
instability, previously whenever the term ’silver nitrofor-
mate’ or similar expressions were used to describe the com-
position of this compound in the solid state, it is likely that
in fact a hydrate was discussed. It was not possible to deter-
mine the sensitivity data of the silver nitroformate hydrates
because of the observed highly explosive nature of these
compounds and the difficulty in determining the precise hy-
drate formed without performing an X-ray structure analy-
sis on the same batch that would be used for obtaining the
sensitivity data.
Figure 11 Structure of the asymmetric unit of AgC(NO2)3·0.5
H2O in the crystal. The thermal ellipsoids are drawn with a proba-
bility factor of 50 %, only the hydrogen atoms are drawn with a
probability factor of 10 % for clarity.
Silver nitroformate hemihydrate crystallizes in the ortho-
rhombic space group Pna21 (no. 33) with four formula units
per unit cell. However, one formula unit consists of two
crystallographically different anions. A view along the a
axis of the unit cell reveals some interesting structural de-
tails.
As was discussed previously for potassium nitroformate,
a wavelike pattern consisting of anions and cations forming
a band was observed for the silver salt. One out of the two
crystallographically different anions can be addressed to
this pattern. The second anion can be addressed to the
structural motif lying in between these bands. A closer look
at the coordination spheres of the two crystallographically
different silver atoms reveals that the silver atoms forming
the wavelike pattern together with the corresponding anions
are not coordinated by water, in contrast to the second sil-
ver atoms which are part of the second structural motive.
Formally this may be considered as a solid solution of the
anhydrous silver salt dissolved in the monohydrate yielding
Figure 12 Unit cell of AgC(NO2)3·0.5 H2O along the a axis. The
thermal ellipsoids are drawn with a probability factor of 50 %, only
the hydrogen atoms are drawn with a probability factor of 10 %
for clarity.
the hemihydrate. The anions again have a planar C-N3 moi-
ety with the sum of NCN angles being 360° and 359.8°,
respectively. While the anion which is coordinated to the
water molecule adopts the commonly observed C2v like
structure, the other anion belongs to the rare conformation
in which all three nitro groups are more evenly twisted rela-
tive to the central plane. The propeller like orientation (D3)
seems to be close to a limit where electronic effects such as
π overlap of the orbitals are balanced by steric effects of
the nitro group.
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M. Göbel, T. M. Klapötke, P. Mayer
Table 1 Crystallographic Data of KC(NO2)3, AgC(NO2)3 ·H2O, and AgC(NO2)3 ·0.5 H2O.
formula
C K N3 O6
189.14
200(2)
C H2 Ag N3 O7
275.93
200(2)
C2 H2 Ag2 N6 O13
533.84
200(2)
orthorhombic
Pna21 (no.33)
8.616(2)
formula weight
temperature / K
crystal system
space group
tetragonal
monoclinic
P21/n (no. 14)
7.5172(2)
7.8572(2)
20.7387(5)
91.396(1)
1224.55(5)
8
¯
I42d (no. 122)
˚
a / A
11.3594(5)
11.3594(5)
8.7883(5)
˚
b / A
8.955 (2)
15.297(3)
˚
c/ A
β / °
volume / A
Z
3
˚
1134.0(1)
8
0.928
2.216
1180.3(4)
4
3.417
3.004
1016
absorption coefficient / mmϪ1
density exptl. / g / cm3
F(000)
3.305
2.993
1056
752
2 theta / °
54.9
50.0
54.97
index ranges
Ϫ12 Յ h Յ 14,
Ϫ14 Յ k Յ 12,
Ϫ11 Յ l Յ 11
4026
644 [R(int. ϭ 0.0569]
52
Ϫ8 Յ h Յ 8,
Ϫ9 Յ k Յ 9,
Ϫ24 Յ l Յ 24
10795
2150 [R(int. ϭ 0.0602]
233
Ϫ11 Յ h Յ 11,
Ϫ11 Յ k Յ 11,
Ϫ19 Յ l Յ 19
14470
2696 [R(int. ϭ 0.0492]
209
reflections collected
reflections unique
parameters
GOOF
R1 / wR2 [I> 2σ(I)]
R1 / wR2 (all data)
1.053
1.167
1.037
0.0273 / 0.0464
0.0443 / 0.0496
0.193
0.0315 / 0.0678
0.0413 / 0.0709
1.281
0.0287 / 0.0517
0.0422 / 0.0558
0.543
Ϫ3
˚
largest res. Peak / e·A
The first silver atom is coordinated by ten oxygen atoms
belonging to six nitroformate anions within a distance of
3.6 A, similar to the coordination of the potassium cation
Table 2 Selected structural parameters of the potassium and silver
salts of nitroform.
˚
Dihedral angle C-N distance Average N-O distance
by the nitroformate anions in the structure of potassium
nitroformate as discussed above. Although in this case there
is no regular coordination polyhedron, similarities exist in
the wheel-like coordination of the silver cation by four
anions which coordinate via two oxygen atoms each and
additional two anions which coordinate through only one
oxygen atom of one nitro group that are orientated along
the anticipated axis of that wheel. Three of the four anions
orientated in the wheel-like conformation show coordi-
nation of the silver cation with two oxygen atoms of one
nitro group each while one of the four anions coordinates
the silver cation twice with one oxygen atom of one nitro
group.
˚
˚
degree
A
A
AgC(NO2)3 ·H2O
N1 9.3(5)
N2 2.4(5)
N3 39.9(5)
N4 46.2(5)
N5 3.0(5)
N6 10.3(4)
1.392(6)
1.383(6)
1.441(6)
1.443(6)
1.382(6)
1.384(6)
1.247(5)
1.248(5)
1.222(5)
1.223(5)
1.243(5)
1.243(5)
AgC(NO2)3 ·0.5 H2O
N1 19.6(8)
1.367(1)
1.400(5)
1.418(1)
1.384(8)
1.366(7)
1.442(5)
1.245(5)
1.227(8)
1.236(5)
1.24(5)
1.247(5)
1.222(7)
N2 32.1(9)
N3 18.9(8)
N4 14.4(6)
N5 10.5(6)
N6 53.9(6)
KC(NO2)3
The second silver atom is coordinated by twelve oxygen
atoms belonging to two water molecules and six nitrofor-
mate anions. So far the coordination of potassium and sil-
ver ions always showed all of the three possible coordi-
nation modes for the oxygen atoms of the nitro groups chel-
ating to the metal ion. This is also true in this last case,
however, there is no coordination polyhedron to describe
this structure or any kind of obvious symmetry that would
help to describe the structure of this complex. It is worth-
while to point out that the three possible different chelating
modes are evenly distributed to the six anions, whereby two
anions coordinate the silver cation with two oxygen atoms
of one nitro group each. Another two anions coordinate the
silver cation twice with one oxygen atom of one nitro group
each and finally, two anions coordinate the silver ion with
only one oxygen atom of one nitro group.
N1 33.8(1)
N2 8.0(1)
N1 33.8(1)
1.415(2)
1.374(3)
1.415(2)
1.236(2)
1.250(2)
1.236(2)
groups works well [5]. A correlation between the length of
the C-N and N-O bonds and the corresponding dihedral
angles can be observed as expected, whereby the C-N bonds
of out-of-plane nitro groups are elongated and C-N bonds
of in-plane nitro groups are shortened. There is also a re-
verse tendency for N-O distances. The structural character-
istics such as bond distances and dihedral angles of the pot-
assium and the silver salts of nitroform are presented in
Table 4, and fall within the range of expected values.
Experimental Section
Considering the relationship of the orientation of the
nitro groups relative to the C-N3 plane it appears that the
relation of bond lengths vs. dihedral angles of the nitro
Caution: Salts of nitroform are energetic materials. Proper protec-
tive measures (safety glasses, face shields, leather coat, earthening
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Potassium and Silver Salts of Nitroform
(equipment and person), KevlarTM gloves and ear plugs) should be
used when handling these materials.
1246 (21), 1168 (7), 873 (35), 794 (11), 719 (7), 465 (8), 442 (3), 283 (6), 257
(14), 155 (12), 113 (8); UV-VIS (Acetone): 349 nm (Eϭ0.525); m/z (FABϪ/
NBA): 150 [C(NO2)3Ϫ, vs], 62 [NO3Ϫ, w], 46 [NO2Ϫ, m]
The thermal behaviour of the salts has been investigated using a
differential scanning calorimeter (Perkin-Elmer Pyris 6 DSC) at
heating rates of 5 °C minϪ1. All reagents and solvents were used
Nitroform, HC(NO2)3
1
as received (Aldrich, Fluka). H, 13C and 14N NMR spectra were
313 mg of KNF (1.66 mmol) were suspended in 2.5 mL of pentane
and cooled with an ice bath. To this suspension 1 mL of concen-
trated sulfuric acid (98 %) was given dropwise over a period of ten
minutes. The sulfuric acid turned yellow at once. After two hours
the color had disappeared and the sulfuric acid was extracted ten
times with 2 mL of pentane. In order to isolate the nitroform as a
white solid, the collected pentane phases were treated with a cur-
rent of nitrogen. Because of the heat of evaporation of pentane it
was ensured that the precipitating white nitroform crystals would
not liquefy andclean product was obtained.
recorded with a Jeol Eclipse 270, Jeol EX 400 or Jeol Eclipse 400
instrument operating at 400 MHz (1H), 100.6 MHz (13C), and
28.9 MHz (14N). All chemical shifts are quoted in ppm relative to
TMS (1H, 13C) or nitromethane (14N). UV-VIS spectra were meas-
ured using a Perkin Elmer Lambda 16 UV-VIS spectrometer. Infra-
red (IR) spectra were recorded using a Perkin-Elmer Spektrum One
FT-IR instrument. Raman spectra were measured using a Perkin
Elmer Spektrum 2000R NIR FT-Raman instrument equipped with
a Nd:YAG laser (1064 nm). Reactions involving silver nitroformate
were carried out using brown glassware and red light as the light
source.
The yield was 157.5 mg (63 %); m.p.: 25.4 °C.
1H NMR (CDCl3) δ: 7.46 (s, 1H, H-C(NO2)3); 13C NMR (CDCl3) δ: 114.4
(sept., 1C, J 8.7 Hz, H-C(NO2)3); 14N NMR (DMSO-d6) δ: Ϫ38.3 (-NO2,
∆ν1/2 ϭ7.2 Hz); ν˜ (gas, Ϫ196 °C defrost) /cmϪ1: 3063 [ν(CH)], 1618 [s,
νas(NO2)], 1608 [s, νas(NO2)], 1303 [s, νs(NO2) antiphase], 947 [w, ν(CN)],
845 [δ(NO2) synphase], 779 [s, δ(NO2) antiphase], 630 [w, w(NO2)], 569
Tetranitromethane, C(NO2)4
[w, w(NO2)]; Raman (100 mW, protection shield, 40 scans, 0 °C, 2 cmϪ1
)
44 mL of 100 % HNO3 (1.08 mol) were filled into a three necked
round bottom flask and cooled with an ice bath. To this, a solution
of 50 mL acetic acid anhydride containing 0.4 mL of sulfuryl chlo-
ride was added dropwise within half an hour. The temperature of
the reaction mixture was kept below 15 °C. Subsequently, 50 mL
of acetic acid anhydride containing 2 mL of sulfuryl chloride were
added to the reaction mixture in the same way. The reaction flask
containing a slight yellow solution was then protected from light
with silver foil and left standing for seven days. Then the solution
was put onto 100 mL of ice water in a separating funnel. Two layers
formed, one yellow upper phase and one colorless phase at the
bottom. The colorless phase was washed ten times with 10 mL of
water and then with 20 mL of a water solution containing ten per-
cent sodium carbonate affording pure tetranitromethane.
ν˜ /cmϪ1: 3029 (25), 2758 (5), 1626 (49), 1611 (24), 1375 (50), 1327 (22), 1309
(36), 1243 (26), 950 (69), 943 (57), 840 (51), 774 (22), 628 (36), 574 (21), 405
(100), 375 (95), 237 (12), 204 (18), 121 (14); m/z (CIϩ, NH3) 152
[(Mϩ1)(0,6)], 105 [(M-NO2)(0,07)], 46 [(NO2)(100)], 30,0 [(NO)(32,6)].
Silver nitroformate monohydrate, AgC(NO2)3·H2O
258 mg of freshly prepared and moist silver oxide (1.11 mmol) were
suspended in 5 mL of water and the suspension was filtered.
146 mg of nitroform (0.97 mmol) were dissolved in 5 mL of freshly
distilled diethylether and cooled with an ice-bath. Freshly filtrated
and moist silver oxidewas then added to this solution while stirring
vigorously. After fifteen minutes, the reaction mixture was filtered
and the solvent removed affording bright yellow crystals. Single
crystals suitable for X-ray structure determination were obtained
by recrystallizing these crystals from water and were immediately
measured. 185 mg of yellow silver nitroformate monohydrate were
obtained (74 % yield). m.p.: 70 °C (decomp. with evolution of gas)
13C NMR (DMSO-d6) δ: 150.4 (C(NO2)3); 14N NMR (DMSO-d6) δ: Ϫ29.9
(-NO2, ∆ν1/2 ϭ13.5 Hz); Raman (100 mW, protection shield, 100 scans,
4 cmϪ1) ν˜ /cmϪ1: 1463 (14), 1379 (78), 1257 (87), 1153 (35), 878 (100), 791
(13), 722 (8), 473 (16), 455 (15), 420 (8), 280 (16), 166 (24); UV-VIS (Ace-
tone): 349 nm (Eϭ0.382); m/z (FABϪ, NBA): 150 [(C(NO2)3Ϫ), vs], 104
[(C(NO2)2Ϫ, w], 46 [(NO2), w].
44.3 g of TNM were obtained which corresponds to a yield of
83.7 % related to HNO3. m.p.: 13.0Ϫ14.0 °C,
13C NMR (DMSO-d6) δ: 161.5 (Cq); 14N NMR (DMSO-d6) δ: Ϫ48.3 (-NO2,
∆ν1/2 ϭ 4.4 Hz); ν˜ (KBr, r.t.)/cmϪ1: Raman (250 mW, protection shield, 50
scans, 2 cmϪ1, r.t.) ν˜ /cmϪ1: 1647 [νas(NO2),(10)], 1615 [νas(NO2),(10)], 1343
[νs (NO2),(18)], 1276 [νs (NO2),(12)], 998 (5), 862 [C-NO2, (100)], 801
[C-NO2, (4)], 605 [δs (NO2),(5)], 414 [δC-N, (18)], 358 [δC-N, (82)], 227
[δC-N, (11)], 197 [δC-N, (12)].
Potassium nitroformate, KC(NO2)3
Potassium hydroxide (111 mg, 2 mmol) and glycerol (183 mg,
2 mmol) were dissolved in 5 mL of water and stirred at ice bath
temperature. To this solution, were added portion-wise over a per-
iod of ten minutes, 130 mg of tetranitromethane (0.66 mmol). The
ice-bath was removed and the reaction mixture was allowed to
warm up to room temperature and stirred for one hour. The pre-
cipitate was filtered off and washed with 2 mL of diethylether. The
mother liquor was used again instead of the 5 mL of water used
initially and the procedure was repeated. Crystals suitable for single
X-ray crystallography were obtained by recrystallizing potassium
nitroformate from nitromethane at room temperature and were
measured immediately. The yield was 180 mg (72 %) of bright yel-
low KNF. m.p.: 83 °C (decomp. with evolution of gas)
Silver nitroformate hemihydrate, AgC(NO2)3·0.5 H2O
The reaction was undertaken as described above for the prep-
aration of silver nitroformate monohydrate. Silver nitroformate
monohydrate was recrystallized from acetic acid anhydride at room
temperature affording single crystals of silver nitroformate hemi-
hydrate. The crystals were immediately cooled to liquid nitrogen
temperature and immediately used for X-ray structure determi-
nation.
X-ray structure determination of [KC(NO2)3],
[AgC(NO2)3·H2O], and [AgC(NO2)3·0.5 H2O]
13C NMR (DMSO-d6) δ: 150.8 (C(NO2)3); 14N NMR (DMSO-d6) δ: Ϫ30.3
(-NO2, ∆ν1/2 ϭ22.3 Hz); Raman (100 mW, protection shield, 60 scans,
4 cmϪ1) ν˜ /cmϪ1: 1508(5), 1466 (3), 1422 (6), 1394 (38), 1291 (34), 1272 (100),
The data in table 1 were collected using a NONIUS KAPPA CCD
diffractometer with a rotating anode using Mo-Kα radiation. The
Z. Anorg. Allg. Chem. 2006, 1043Ϫ1050
 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
1049

M. Göbel, T. M. Klapötke, P. Mayer
structures were solved with direct methods by applying the program
SIR 97 [26]; for the refinement the program SHELX 97 was used.
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40b, 906.
Further details on the crystal structure investigation may be ob-
tained from the Fachinformationszentrum Karslruhe, 76344 Egg-
enstein-Leopoldshafen, Germany (fax: (ϩ49) 7247-808-606; e-mail:
crysdata@fiz-karlsruhe.de), on quoting the depository numbers
CSD 416069 KC(NO2)3, CSD 416070 AgC(NO2)3·H2O and CSD
416068 [AgC(NO2)3·0.5 H2O].
Acknowledgements. We thank Priv.-Doz. Dr. K. Karaghiosoff for
carrying out the NMR experiments as well as Dr. G. Fischer for
measuring the mass spectra. Prof. Dr. P. Klüfers is thanked for a
generous allocation of X-ray diffractometer measuring time. We are
indebted to and thank Dr. habil. M.-J. Crawford for many inspired
discussions and for her help with improving this manuscript. We
are grateful to the Cusanuswerk for a scholarship to M. Göbel.
Ludwig-Maximilan University, the Fonds der Chemischen
Industrie and Diehl BGT Defence GmbH & Co. KG are thanked
for generous financial support.
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skii, V. V. Mel’nikov, Zh. Strukt. Khim. (Russ.) (J. Struct.
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