Cyanidosilicates—Synthesis and Structure

Article abstract of DOI:10.1002/anie.201901173

Starting from fluoridosilicate precursors in neat cyanotrimethylsilane, Me₃Si?CN, a series of different ammonium salts [R₃NMe]⁺ (R=Et, ⁿPr, ⁿBu) with the novel [SiF(CN)₅]^2? and [Si(CN)₆]^2? dianions was synthesized in facile, temperature controlled F^?/CN^? exchange reactions. Utilizing decomposable, non-innocent cations, such as [R₃NH]⁺, it was possible to generate metal salts of the type M₂[Si(CN)₆] (M⁺=Li⁺, K⁺) via neutralization reactions with the corresponding metal hydroxides. The ionic liquid [BMIm]₂[Si(CN)₆] (m.p.=72 °C, BMIm=1-butyl-3-methylimidazolium) was obtained by a salt metathesis reaction. All the synthesized salts could be isolated in good yields and were fully characterized.

Full text of DOI:10.1002/anie.201901173

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Cyanidosilicates – Synthesis and Structure
Authors: Axel Schulz, Jörg Harloff, Dirk Michalik, Simon Nier, Philip
Stoer, and Alexander Villinger
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201901173
Angew. Chem. 10.1002/ange.201901173
Link to VoR: http://dx.doi.org/10.1002/anie.201901173
http://dx.doi.org/10.1002/ange.201901173

10.1002/anie.201901173
Angewandte Chemie International Edition
COMMUNICATION
Cyanidosilicates – Synthesis and Structure
Jörg Harloff,[a] Dirk Michalik,[a,b] Simon Nier,[a] Axel Schulz,*[a,b] Philip Stoer,[a] and Alexander Villinger[a]
Abstract: Starting from fluoridosilicate precursors in neat cyano-
trimethylsilane, Me3Si-CN, a series of different ammonium salts
[R3NMe]+ (R = Et, nPr, nBu) with the novel [SiF(CN)5]2− and [Si(CN)6]2−
dianions were synthesized in facile, temperature controlled F− / CN−
exchange reactions. Utilizing decomposable, non-innocent cations
such as [R3NH]+, it was possible to generate metal salts of the type
M2[Si(CN)6] (M+ = Li+, K+) via neutralization reactions with the corres-
ponding metal hydroxides. The ionic liquid [BMIm]2[Si(CN)6] (m. p. =
72 °C, BMIm = 1-butyl-3-methylimidazolium) was obtained by salt
metathesis reaction. All synthesized salts could be isolated in good
yields and were fully characterized.
spectroscopy (δ = −130 ppm).[34] Later, Dixon and co-workers
were able to synthesize and isolate [nBu4N][Me3Si(CN)2] from a
solution of [nBu4N]CN and Me3Si-CN.[32] Interestingly,
[Me3SiF(CN)]− ions were discussed as strong nucleophilic
cyanide source for SN2 reactions,[35] while [Me3Si(CN)2]− and
[Me3Si(CN)Cl]− were reported to be the active species in the
enantioselective cyanosilylation reactions of aldehydes and
ketones.[26,28,30,33] Astonishingly, no salts bearing the hexacoor-
dinated cyanidosilicate dianions, [Si(CN)6]2–, are known, although
the analogous hexapseudohalogenido silicates of the azide,[36]
(iso)cyanate,[37,38] and thiocyanate[39] were isolated. Moreover,
Fehlhammer et al. reported vibrational data on a suggested
[Si{NCCr(CO)5}6]2– ion featuring an Si(NC)6 core. Following our
interest in pseudohalogen chemistry,[40] in particular the
cyanide / halogenide exchange reactions,[41,42] we want to report
on the successful synthesis of salts containing the [SiF(CN)5]2–
and [Si(CN)6]2– dianions and close this gap in main group
chemistry.
In a first series of experiments, we tried to synthesize the
[Si(CN)6]2− dianion by treating an acetonitrile solution of SiCl4 with
two equivalents of [WCC]CN and four equivalents of AgCN as
depicted in Scheme 1 (WCC = weakly coordinating cation).[43] All
attempts failed with respect to complete hexa-substitution, even
upon using a large excess of both cyanido sources, since only
partial CN– / Cl– exchange was observed as monitored by 13C and
29Si NMR studies. For example, we were able to isolate a silicate
with the composition [Ph4P]2[SiCl0.78(CN)5.22] ∙ 4 CH3CN or when
a large excess of AgCN was used, a silver salt containing a
[AgCl(CN)]– ion was obtained (see ESI, Figure S13). By this
method we always obtained chloride / cyanide mixtures with a
maximum of five cyanido ligands (Figure 1 left). Therefore, we had
to change our synthesis strategy and switched to hexafluorido-
silicates[44–46] as starting materials.
Little is known about neutral binary Si-CN compounds (e.g. Si-CN
and Si(CN)2),[1–7] which were studied in an argon matrix or
observed in the envelope of a star,[1,3,8] although cyanide-
containing silanes such as the cyanotrimethylsilane (Me3Si–CN)
are well-known in organic chemistry for their versatile use as
cyanosilylation reagent in combination with Lewis acids or
bases.[9–14] The higher substituted dicyanodimethylsiliane can be
used as protective reagent,[15–17] whereas the tricyanomethyl-
silane has not been isolated yet, but was assumed to be formed
in situ in a reaction of MeSiCl3 with KCN.[18] So far, binary Si(CN)4
has not been synthesized, only a few geometry calculations were
published.[19,20] It has been shown that Me3Si-CN is a particularly
valuable reagent for fluorido / cyanido exchange reactions, which
serves, for example, for the synthesis of cyanidoborates
([B(CN)4-nFn]–,[21–23] n = 0 - 3) as well as phosphates ([P(CN)6-nFn]–,
n = 1 - 5).[24] These reactions are thermodynamically favored due
to the formation of fluorotrimethylsilane (Me3Si-F) that exhibits a
strong Si-F bond with an high bond dissociation energy (57617
kJ mol–1).[25] In addition, the equilibrium of the exchange reaction
can be influenced by either using Me3Si-CN in large excess or by
distilling off Me3Si-F under standard conditions (b.p. 16.0 °C). It
was also shown that Lewis acids such as GaCl3 can significantly
accelerate F– / CN– exchange reactions and also allow working at
lower temperatures.[22,23] Only less is known about pentacoor-
dinated silicate monoanions, which contain cyanido ligands.[26–35]
The first observation dates back to 1980, when Brownstein spec-
troscopically detected the [SiF4(CN)]− anion by means of 19F NMR
2 [WCC]CN + 4 AgCN + SiCl4
2 [WCC]CN + 4 AgCN + SiCl4
[WCC]2[Si(CN)6] + 4 AgCl
[WCC]2[SiCl4-n(CN)2+n] ...
CH3CN
n = 0-3

+ [WCC][Cl-Ag-CN] + AgCl
Scheme 1. Reaction of [WCC]CN and AgCN with SiCl4 ([WCC]+ = [Ph4P]+,
[nPr3NMe]+).
[a]
Prof. Dr. Axel Schulz, Dr. Jörg Harloff, Dr. Dirk Michalik, Simon Nier,
Philip Stoer, Dr. Alexander Villinger,
First of all, we had to find a suitable synthesis strategy for the
production of alkyl-substituted hexafluoridosilicates of the type
[R4N]2[SiF6] or [R3NH]2[SiF6]. As shown in Scheme 2, two different
synthesis pathways (A and B) were followed: On the one hand,
the amines NR3 (R = ethyl, n-propyl) were directly reacted with
aqueous hexafluorosilicic acid, H2SiF6, which led to the formation
of the corresponding [R3NH]2[SiF6] salts in good yields (ca. 70%
route A). On the other hand, ammonium-methyl carbonates, ionic
liquids with a decomposable anion,[47–52] were treated with
aqueous H2SiF6, which resulted in the formation of tetra-alkylated
ammonium salts [R3NMe]2[SiF6] (R = ethyl, n-propyl, and n-butyl)
Institut für Chemie, Universität Rostock
Albert-Einstein-Str. 3a, 18059 Rostock, Germany
Fax: +49-(0)381/498-6382
E-mail: axel.schulz@uni-rostock.de
Homepage: http://www.schulz.chemie.uni-rostock.de/
Prof. Dr. Axel Schulz
Abteilung Materialdesign, Leibniz-Institut für Katalyse e.V. an der
Universität Rostock
Albert-Einstein-Str. 29a, 18059 Rostock, Germany
[b]
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201901173
Angewandte Chemie International Edition
COMMUNICATION
in very good yields (90%). We would like to point out that we
always observed (according to 19F NMR experiments) highly dy-
namic mixtures of [SiF6]2–, [SiF5]– and F– in solution (Figure S30),
regardless of whether synthesis route A or B was chosen. There-
fore, only corresponding mixtures were isolated in the solid.
[SiF(CN)5]2– and [Si(CN)6]2– salts was unequivocally proven by
single crystal X-ray diffraction.
Starting from [R3NMe]2[Si(CN)6] salts, we next attempted to
produce metal-cyanidosilicate salts by salt metathesis reaction.
For example, AgNO3 was reacted with [nBu3NMe]2[Si(CN)6] in
CH3CN. This reaction failed because insoluble silver cyanide or
Ag-CN-complex salts were always formed immediately, for
example {[Ag(PPh3)3]2(CN)}[Ag(CN)2] · 3 CH3CN, which could be
clearly proven by single crystal structure analysis (Table S8,
Figure S11). The great advantage of [R3NH]2[Si(CN)6] over
[R3NMe]2[Si(CN)6] salts is that the former have a decomposable,
non-innocent cation.[23,24] Therefore, these salts are particularly
suitable for the synthesis of metal salts by reacting them with
corresponding metal bases as illustrated in Scheme 3 (eq. 1). By
this procedure, M2[Si(CN)6] (M = Li, K) could be obtained in good
to very good yields (68 - 90%) and fully characterized (Figures
2 - 3). [BMIm]2[Si(CN)6] was synthesized in a salt metathesis
reaction with K2[Si(CN)6] utilizing a biphasic system of water and
dichloromethane (yield 91%, eq. 2, Scheme 3).[53]
2 R3N + H2SiF6
rt
[R3NH]2[SiF(CN)5]
-5 Me Si-F
3
A
[R3NH]2[SiF6] + Me3Si-CN(ex.)
100 °C
[R3NH]2[Si(CN)6]
-6 Me Si-F
3
2 [R3NMe][CO3Me] + H2SiF6
-2 CO , -2 MeOH
2
rt
[R3NMe]2[SiF(CN)5]
-5 Me Si-F
3
B
[R3NMe]2[SiF6] + Me3Si-CN(ex.)
100 °C
[R3NMe]2[Si(CN)6]
-6 Me Si-F
3
Scheme 2. Synthesis of [R3NH]2[SiF6] and [R3NMe]2[SiF6] as well as their
conversion to [R3NH]2[SiF(CN)5] / [R3NH]2[Si(CN)6] and [R3NMe]2[SiF(CN)5] /
[R3NMe]2[Si(CN)6] (R = ethyl, n-propyl, and n-butyl). For reasons of clarity, the
[SiF5]– impurities in the starting materials were omitted (see ESI).
25 °C
H2O
(1)
(2)
M2[Si(CN)6] + 2 R3N + H2O
[BMIm]2[Si(CN)6] + 2 KBr
[R3NH]2[Si(CN)6] + 2 MOH
K2[Si(CN)6] + 2 [BMIm]Br
25 °C
H2O/CH2Cl2

[nPr3NH]2[Si(CN)6]
2 HCN + 2 nPr3N + Si(CN)4
(3)
With hexafluoridosilicates in hand, we were now able to work
with cyanotrimethylsilane, Me3Si-CN, as cyanation reagent that
was always used in a 20-fold excess compared to the [SiF6]2– salt.
Interestingly, when the reactions were carried out at 25 °C for 2h,
we always obtained salts containing the [SiF(CN)5]2– ion (besides
traces of hexacyanidosilicate [Si(CN)6]2–) in moderate yields
(50 - 60%). However, when the temperature was increased to
100 °C, the reaction led to the formation of [Si(CN)6]2– salts in very
good yields (60 - 90%) with a reaction time of 2h. With small
amounts of GaCl3 as Lewis acid catalyst added to the reaction
mixture, the reaction time can be shortened.[22,23] In addition, sig-
nificantly fewer traces of [SiF(CN)5]2– ions were detected. The pro-
gress of these stepwise cyanation reactions was readily moni-
tored by 19F NMR experiments in CH3CN (Figure S83). For exam-
ple, after one minute small amounts of Me3Si-F ([19F] = –157),
[SiF(CN)5]2– (–75), [SiF2(CN)4]2– (–89), [SiF3(CN)3]2– (–109) as
well as large amounts of [SiF6]2– (–127 ppm, see also Table S14)
were detected. With increasing reaction time, the amount of
Scheme 3. Eq. 1: synthesis of M2[Si(CN)6] (M = Li, K), eq. 2: synthesis of
[BMIm]2[Si(CN)6] and eq. 3: decomposition of [R3NH]2[Si(CN)6] upon thermal
treatment.
Table 1. Selected spectroscopic data (Tdec in °C, CN in cm–1) along with data
from ESI-TOF experiments (cat/an = cation/anion of the considered species).
[a]
species
Tdec
NI-ESI[b]
PI-ESI[b]
CN
[nPr3NMe]2[SiF(CN)
yield = 50 %
175
2172
(2177)
[Si(CN)4F]
[Si(CN)5]−
[d]
[nPr3NMe]2[SiF(CN)
yield = 56 %
170
200
140
176
260
219
2170
[Si(CN)4F]
[Si(CN)5]−
[Si(CN)5]−
{cat3an1}+
(2173)
[nBu3NMe]2[Si(CN)6]
yield = 66 %
2164
{cat3an1}+
(2173)
2170
[Et3NH]2[Si(CN)6]
yield = 91 %
[Si(CN)5]−
[Si(CN)5]−
[Si(CN)5]−
[Si(CN)5]−
{cat2[Si(CN)5]}+
Me3Si-F and [SiF(CN)5]2– increases significantly. By means of 13
C
(2171)
{cat3[Si(CN)5]2}+
and 29Si(IG) NMR experiments, the formation of [Si(CN)6]2–
([13C] = 140.0 s; [29Si] = –307 s) was proven compared to
[SiF(CN)5]2– ([13C] = 141.6 d, 140.3 d; [29Si] = –273 d). Interes-
tingly, when no solvent was used, the conversion to [SiF(CN)5]2–
at ambient temperature was complete after 1h, which was not the
case, when a solvent such as CH3CN was used. For this reason,
all reactions were carried out without solvent and hence the
reaction medium can be regarded as a mixture with the charac-
teristics of an ionic liquid. Work-up included removing of all vola-
tiles such as Me3Si-X (X = F, CN) and re-crystallization from
acetonitrile that led usually to the formation of crystals suitable for
structure elucidation (see ESI Tables S1 - S13 and ORTEP-
Figures S1 - S15). As depicted in Figure 1, the formation of
[nPr3NH]2[Si(CN)6]
yield = 50 %
2170
[d]
(2172)
[d]
Li2[Si(CN)6]
yield = 62 %
K2[Si(CN)6]
yield = 68 %
2282
(2206)
2185
{cat3an1}+
(2189)
[d]
[BMIm]2[Si(CN)6]
Yield = 91 %
220
2168
[Si(CN)5]−
{cat3an2}−
[c]
(2173)
[a] most intensive IR (Raman) band; [b] species found in NI / PI - ESI: negative /
positive-ion electron spray ionization, [c] melting point: 72°, [d] no ion pair found
This article is protected by copyright. All rights reserved.

10.1002/anie.201901173
Angewandte Chemie International Edition
COMMUNICATION
Spectroscopic data of synthesized cyanidosilicate species are
summarized in Table 1. All isolated cyanidosilicates were thermal-
ly stable up to 140 °C. Interestingly, the [BMIm]+ salt melted at
72 °C and did not start to decompose until 220 °C. Thus, it can be
referred to as ionic liquid. As expected, cyanidosilicates con-
taining the decomposable [R3NH]+ ions were considerably less
stable than the [R4N]+ / M+ salts. Combined IR and TGA experi-
ments of [nPr3NH]2[Si(CN)6] showed that, as expected, this salt
decomposed into free amine nPr3N(g), HCN(g) and Si(CN)4(g) at
temperatures above 176 °C (eq. 3 in Scheme 3, Figure S79). By
means of ESI-TOF measurements, it was possible to observe
either the [SiF(CN)4]– or [Si(CN)5]– monoanions in case of the
[SiF(CN)5]2– salts, while for all [Si(CN)6]2– salts always the
[Si(CN)5]− monoanion was detected in the negative mode. Only
for [BMIm]2[Si(CN)6], we were able to observe a larger cluster ion
{[BMIm]3[Si(CN)6]2}−, indicating that this species can be trans-
ferred into the gas phase without decomposing the [Si(CN)6]2–
dianion. In the positive mode it was possible to detect singly
charged salt cluster ions of the composition {cat2[Si(CN)5]}+,
{cat3[Si(CN)5]2}+, containing a formal [Si(CN)5]– moiety, and both
the {cat3[Si(CN)5F]}+ and the {cat3[Si(CN)6]}+ for some of the
studied species (Table 1, cat = specific cation).[54,55]
troscopic investigation of the strong acidic solution (pH = 1) re-
vealed a new signal for the proton at 4.3 ppm in 1H NMR spectra
and a still intact [Si(CN)6]2− ion according to 13C NMR experiments
(Figure S80). The isolation of the free acid in the form of a solid
was not successful until now, because the slow evaporation of the
solution in a desiccator or the much faster removal of all volatile
components in vacuum only led to decomposition caused by the
loss of HCN.
All structure determinations of the ammonium silicate salts
unequivocally proved the presence of either almost C4v sym-
metrical [SiX(CN)5]2– (X = F, Cl) or octahedral [Si(CN)6]2– anions
(Figure 1), featuring both a hexacoordinated silicon atom with
bond angles close to 90 and 180° (Figure 1, Table S13 and
Figures S1-13). These structures consist of separated ions with
no significant interionic contacts as expected for a weakly
coordinating cation, that is, the silicate dianions are surrounded
by the [WCC]+ ions and vice versa (e.g. see Figures S2 and S4).
Both the Si-Cl (2.24(2) Å) and the Si-F (1.68(1) Å) bond lengths
are in the expected range of a Si-X single bond (cf. rcov (Si-X),[56]
1.78 X = F and 2.15 Å X = Cl). The experimentally determined Si-
C bond lengths for the [SiCl(CN)5]2– ion is also in the range for a
single bond (average 1.945 Å), in accord with those found for
[SiF(CN)5]2– (average 1.951 Å) and [Si(CN)6]2– (1.952 Å, cf. rcov
(Si-C) = 1.91 Å).[56] Since the [Si(CN)6]2– ion is able to form
coordination polymers by coordinating with Lewis acidic cen-
ters,[57] it was of interest to crystallize metal salts and investigate
their structures (e.g. Li+ and K+).
Figure 1. Ball-and-stick representation of the molecular anion structure in the
crystal: Left: [Ph4P]2[SiCl0.78(CN)5.22] ∙ 4 CH3CN. Middle: [nPr3NH]2[SiF(CN)5],
Right: [nPr3NH]2[Si(CN)6]. Cations and solvent molecules are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Left: Si-Cl 2.24(2), Si-C1 1.929(5), Si-
C2 1.94(1), Si-C3 1.967(8); Cl-Si-C2 177.060(7), Cl-Si-C3 89.954(6), C2-Si-C3
90.989(7). Middle: Si-F 1.68(1), Si-C1 1.914(9), Si-C2 1.965(9), Si-C5 1.95(2);
F-Si-C5 178.9(9), F-Si-C1 92.5(5), C1-Si-C2 88.8(4), C1-Si-C3 177.7(4). Right:
Si-C1 1.952(1), C1-Si-C1' 91.24(5), C1-Si-C1'' 88.76(5), C11-Si-C1'' 180.0.
Symmetry code: (') 1-y, 1-z, 1-x, ('') y, z, x.
Next, we investigated the stability towards moisture, mineral
acids and bases. It should be noted that a typical, but weak odour
of hydrogen cyanide (HCN) was noticed when adding water to a
prepared NMR sample. However, a signal for free HCN ([13C] =
113 ppm) was only observed after four days and even then most
of the [Si(CN)6]2− species remained intact. Besides, instant and
strong release of HCN(g) could be detected by a BW GasAlert
Detector when a droplet of concentrated aqueous HCl (12 M) was
added to solid [Et3NH]2[Si(CN)6]. When using less concentrated
HCl (0.1 M) evolution of HCN was observed as well, but the anion
decomposed much slower and even after two days, most of the
[Si(CN)6]2− could still be observed beside a small signal for HCN
according to time-dependent 13C NMR studies, even at slightly
elevated temperatures (50°C, see Figure S82). Encouraged by
Figure 2. Ball-and-stick representation of a section of the molecular structure in
in the crystal of Li2[Si(CN)6] · 2 H2O. Hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Si-C1 1.947(1), Li1-N1 2.40(2), Li1-
O1 1.913(4); C1-Si-C1' 180.0, N1-Li1-N1'' 102.2(1). Symmetry code: (') –x + y,
-x, z; ('') x - y, 1 - y, -z; (''') 1 - x, 1 – x + y, -z.
Crystals of Li2[Si(CN)6] · 2 H2O suitable for X-ray analysis
were received by slow evaporation of a concentrated solution of
water in the desiccator (Figure 2). Colourless crystals of
̅
Li2[Si(CN)6] · 2 H2O crystallized in the trigonal space group P3m1
with one formula unit per cell. The octahedral [Si(CN)6]2– ion
coordinates to six different Li+ ions, while the distorted tetra-
hedrally coordinated Li+ ion is linked via the N atom of the cyanido
ligand with three different adjacent [Si(CN)6]2– ions besides one
water molecule. These coordination modes lead to the formation
+
this result and in the hope to be able to isolate a H3O+ or H5O2
salt, K2[Si(CN)6] dissolved in water was rinsed over a column filled
with the protic cation exchange resin Amberlyst-15. NMR spec-
This article is protected by copyright. All rights reserved.

10.1002/anie.201901173
Angewandte Chemie International Edition
COMMUNICATION
of planar 12-membered Li2Si2(CN)4 rings, which are connected
either perpendicularly (edge shared at silicon) or coplanar (corner
shared). The Si-C bonds are in the expected range (Si-C1
1.947(1), cf. rcov (Si-C) = 1.91 Å), while the Li-N donor acceptor
bonds are slightly elongated (d(Li1-N1) = 2.40(2), rcov(Li-N) =
from [SiF6]2– at 298 K using the PBE1PBE-D3BJ/aug-cc-pVTZ
level of theory (for details see ESI). Experimentally, we could
show that salts, bearing the [Si(CN)6]2– dianion, can be prepared
from [SiF6]2– and Me3Si-CN and in agreement with these results
the gas phase Gibbs energies for the consecutive substitution
reactions of the first four steps are exergonic, decreasing for
n = 1 - 4 (RG°298: –5.71, –3.01, –1.70, –0.72 kcal mol–1), but
slightly endergonic for n = 5 - 6 (1.56 and 3.51 kcal mol–1, Tables
S15 - 16). It should be noted that, although the last two steps are
slightly endergonic, the reaction was carried out with a 20-fold
excess of Me3Si-CN and the generated Me3Si-F was removed
constantly from the equilibrium, thereby allowing the formation
[SiF(CN)5]2– and [Si(CN)6]2– ions.
2.04 Å,[56] cf. 2.06
Å
in LiCN).[58] Colourless crystals of
K2[Si(CN)6] · 6 CH3CN were obtained after re-crystallization from
acetonitrile. They crystallized in the monoclinic space group P21/n
with two formula units per unit cell. The [Si(CN)6]2– is octahedrally
surrounded by six K+ ions and always linked by the nitrogen atom.
As depicted in Figure 3, each K+ ion coordinates via three nitrogen
atoms of three adjacent cyanido ligands to three different
[Si(CN)6]2– anions (d(K-Nanion) between 2.766(1) - 2.790(1) Å), in
addition to three further, slightly longer K+···NC-CH3 donor-accep-
tor bonds (d(K-Nacetonitrile) between 2.819(7) - 2.933(2) Å). Hence,
the coordination around K+ is best described as [3 + 3] coor-
dination mode with a strongly distorted KN6 core (∡(N1-K-N2) =
159.42(3), ∡(N3-K-N5) = 166.1(2), ∡(N6-K-N4) = 174.1(6) °). The
main structural motif consists of edge linked 12-membered and
18-membered rings, finally leading to the formation of a 3d net-
work, in which the acetonitrile molecules are located inside the
large pores (dpore = 10.4 Å, Figure 3 bottom, Figure S10).
In conclusion, we present here a facile, high yield synthesis
and isolation of salts featuring air stable [SiF(CN)5]2– and
[Si(CN)6]2– dianions, respectively. However, as soon as a drop of
water or an undried polar solvent are added, the smell of HCN
can be perceived. Salts with completely alkylated ammonium
cations and one-proton-containing ammonium cations of the
general formula [R3NR']+ (R = Et, nPr, nBu; R' = H, Me) were
isolated and fully characterized. In particular the [R3NH]+ salts,
containing decomposable anions, can be utilized to generate
easily metal hexacyanidosilicates simply by using metal bases
such as MOH, which leads to the decomposition of the ammonium
ion into R3N and water as well as the formation of M2[Si(CN)6]
salts. The [Si(CN)6]2– ion could also be utilized for the synthesis of
[BMIm]2[Si(CN)6], an ionic liquid, and as building block for the
design of coordination polymers, when Lewis acidic metals were
used as counter ions. Therefore, we expect that salts, containing
[SiF(CN)5]2– or [Si(CN)6]2– dianions, could be applied as electro-
lytes, new coordination building blocks for the design of
coordination polymers, and for studies of fundamental physical
properties (e.g. magnetic properties) with transition metal ions as
counter ions.
Experimental Section
Caution! HCN as well as Me3Si-CN are highly toxic! Appropriate safety
precautions (HCN detector, gas mask, low temperatures) should be taken.
Experimental details including all spectra and ORTEP representations can
be found in the supporting information.
Acknowledgements
The authors thank Deutsche Forschungsgemeinschaft (DFG
SCHU 1170/9-1), especially the priority program SPP 1708 for
financial support.
Figure 3. Top: Ball-and-stick representation of a section of the molecular
structure in the crystal of K2[Si(CN)6] · 6 CH3CN. View of the unit cell along [100].
Selected bond lengths [Å] and angles [°]: Si-C1 1.946(1), Si-C2 1.9427, Si-C3
1.949(1), K-N1 2.766(1), K-N2 2.776(1), K-N3 2.790(1), K-N4 2.933(2), K-N5
2.819(7), K-N6 2.848(2); C-Si-C 180.0, N1-K-N2 159.42(3), N3-K-N5 166.1(2),
N6-K-N4 174.1(6). Symmetry codes: (') –0.5 + x, 0.5 - y, 0.5 + z; ('') 0.5 - x, 1.5
+ y, 1.5 - z.
Keywords: cyanides • silicates • ionic liquids • structure •
synthesis
[1]
[2]
M. Guélin, J. Cernicharo, C. Kahone, J. Gomez-Gonzalez, Astron.
Astrophys. 1986, 157, L17.
G. Maier, H. P. Reisenauer, Eur. J. Org. Chem. 2005, 2005, 2015–
2021.
Finally, we have computed the standard Gibbs energies,
RG°298, for the stepwise formation of the [Si(CN)6]2– ion starting
This article is protected by copyright. All rights reserved.

10.1002/anie.201901173
Angewandte Chemie International Edition
COMMUNICATION
[3]
[4]
S. K. Mandal, H. W. Roesky, Chem. Commun. 2010, 46, 6016.
M. Fukushima, T. Ishiwata, J. Phys. Chem. A 2013, 117, 9435–
9443.
[31]
[32]
[33]
W. H. Stevenson, S. Wilson, J. C. Martin, W. B. Farnham, J. Am.
Chem. Soc. 1985, 107, 6340–6352.
D. A. Dixon, W. R. Hertler, D. B. Chase, W. B. Farnham, F.
Davidson, Inorg. Chem. 1988, 27, 4012–4018.
[5]
[6]
[7]
[8]
G. Maier, H. P. Reisenauer, H. Egenolf, J. Glatthaar, Eur. J. Org.
Chem. 1998, 1998, 1307–1311.
M. Hatano, K. Yamakawa, T. Kawai, T. Horibe, K. Ishihara, Angew.
Chem. Int. Ed. 2016, 55, 4021–4025.
M. C. McCarthy, A. J. Apponi, C. A. Gottlieb, P. Thaddeus, J. Chem.
Phys. 2001, 115, 870–877.
[34]
[35]
S. Brownstein, Canad. J. Chem 1980, 58, 1407–1411.
E. D. Soli, A. S. Manoso, M. C. Patterson, P. DeShong, D. A. Favor,
R. Hirschmann, A. B. Smith, J. Org. Chem. 1999, 64, 3171–3177.
A. C. Filippou, P. Portius, G. Schnakenburg, J. Am. Chem. Soc.
2002, 124, 12396–12397.
N. A. Richardson, Y. Yamaguchi, H. F. Schaefer, J. Chem. Phys.
2003, 119, 12946–12955.
M. Guélin, S. Muller, J. Cernicharo, M. C. McCarthy, P. Thaddeus,
Astron. Astrophys. 2004, 426, L49–L52.
[36]
[37]
[9]
I. M. Reid, C. J. Roberts, 1979, 3, 113–119.
W. C. Groutas, in Encycl. Reagents Org. Synth., John Wiley &
Sons, Ltd, Chichester, UK, 2006, pp. 1–6.
O. Seiler, C. Burschka, K. Götz, M. Kaupp, S. Metz, R. Tacke, Z.
Anorg. Allg. Chem. 2007, 633, 2667–2670.
[10]
[38]
[39]
P. Portius, M. Davis, Dalt. Trans. 2010, 39, 527–532.
O. Seiler, R. Bertermann, N. Buggisch, C. Burschka, M. Penka, D.
Tebbe, R. Tacke, Z. Anorg. Allg. Chem. 2003, 629, 1403–1411.
H. Brand, P. Mayer, A. Schulz, T. Soller, A. Villinger, Chem. – An
Asian J. 2008, 3, 1050–1058.
[11]
[12]
M. R. Booth, S. G. Frankiss, Anal. Proc. 1968, 1347–1348.
M. North, M. Omedes-Pujol, C. Young, Org. Biomol. Chem. 2012,
10, 4289–4298.
[40]
[41]
[42]
[43]
[44]
[13]
[14]
I. Kalikhman, B. Gostevskii, E. Kertsnus, M. Botoshansky, C. A.
Tessier, W. J. Youngs, S. Deuerlein, D. Stalke, D. Kost,
Organometallics 2007, 26, 2652–2658.
K. Bläsing, J. Bresien, R. Labbow, A. Schulz, A. Villinger, Angew.
Chem. Int. Ed. 2018, 57, 9170–9175.
T. A. Bither, W. H. Knoth, R. V. Lindsey, W. H. Sharkey, J. Am.
Chem. Soc. 1958, 80, 4151–4153.
S. Arlt, J. Harloff, A. Schulz, A. Stoffers, A. Villinger, Chem. Eur. J.
2016, 22, 16012–16016.
[15]
[16]
K. Mai, G. Patil, J. Org. Chem. 1986, 51, 3545–3548.
I. Ryu, in Encycl. Reagents Org. Synth., John Wiley & Sons, Ltd,
Chichester, UK, 2001, pp. 5–6.
R. Campbell, M. F. Davis, M. Fazakerley, P. Portius, Chem. Eur. J.
2015, 21, 18690–18698.
J. Aigueperse, P. Mollard, D. Devilliers, M. Chemla, R. Faron, R.
Romano, J. P. Cuer, in Ullmann’s Encycl. Ind. Chem., Wiley-VCH
Verlag GmbH & Co. KGaA, Weinheim, Germany, 2000.
A. Ouasri, A. Rhandour, M. C. Dhamelincourt, P. Dhamelincourt, A.
Mazzah, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 2003,
59, 851–857.
[17]
[18]
I. Ryu, S. Murai, A. Shinonaga, T. Horiike, N. Sonoda, J. Org.
Chem. 1978, 43, 780–782.
F. Duboudin, P. Cazeau, O. Babot, F. Moulines, Tetrahedron Lett.
1983, 24, 4335–4336.
[45]
[19]
[20]
C. Glidewell, J. Organomet. Chem. 1981, 217, 11–18.
J. George, R. Dronskowski, J. Phys. Chem. A 2017, 121, 1381–
1387.
[46]
[47]
J. Fábry, J. Chval, V. Petříček, IUCr, Acta Cryst. Sect. E 2001, 57,
i90–i91.
[21]
[22]
[23]
E. Bernhardt, M. Berkei, H. Willner, M. Schürmann, Z. Anorg. Allg.
Chem. 2003, 629, 677–685.
Z. Q. Zheng, J. Wang, T. H. Wu, X. P. Zhou, Adv. Synth. Catal.
2007, 349, 1095–1101.
K. Bläsing, S. Ellinger, J. Harloff, A. Schulz, K. Sievert, C. Täschler,
A. Villinger, C. Zur Täschler, Chem. Eur. J. 2016, 22, 4175–4188.
K. Bläsing, S. Ellinger, J. Harloff, A. Schulz, K. Sievert, C. Täschler,
A. Villinger, C. Zur Täschler, Eur. J. Inorg. Chem. 2016, 2016,
1175–1183.
[48]
[49]
G. Thielemann, S. Spange, New J. Chem. 2017, 41, 8561–8567.
J. D. Holbrey, R. D. Rogers, S. S. Shukla, C. D. Wilfred, Green
Chem. 2010, 12, 407–413.
[50]
T. N. Glasnov, J. D. Holbrey, C. O. Kappe, K. R. Seddon, T. Yan,
Green Chem. 2012, 14, 3071–3076.
[24]
J. Bresien, S. Ellinger, J. Harloff, A. Schulz, K. Sievert, A. Stoffers,
C. Täschler, A. Villinger, C. Zur Täschler, Angew. Chem. Int. Ed.
2015, 54, 4474–4477.
[51]
[52]
L. H. Finger, J. Sundermeyer, Chem. Eur. J. 2016, 22, 4218–4230.
M. Jost, L. H. Finger, J. Sundermeyer, C. von Hänisch, Chem.
Commun. 2016, 52, 11646–11648.
[25]
[26]
Y.-R. Luo, Y.-R. Luo, Comprehensive Handbook of Chemical Bond
Energies, CRC Press, 2007.
[53]
When a Mixture of water/CH2Cl2 was used as solvent,
[Pr3(ClCH2)N][Si(CN)6] was obtained in small yields (see X-Ray data
Table S9 and Figure S12), indicating HCl elimination.
K. O. Börnsen, Mass Spectrom. Proteins Pept. 2014, 387–404.
C. Hao, R. E. March, T. R. Croley, J. C. Smith, S. P. Rafferty, J.
Mass Spectrom. 2001, 36, 79–96.
H. S. Wilkinson, P. T. Grover, C. P. Vandenbossche, R. P. Bakale,
N. N. Bhongle, S. A. Wald, C. H. Senanayake, Org. Lett. 2001, 3,
553–556.
[54]
[55]
[27]
[28]
[29]
[30]
N. Kurono, M. Yamaguchi, K. Suzuki, T. Ohkuma, J. Org. Chem.
2005, 70, 6530–6532.
[56]
[57]
P. Pyykkö, M. Atsumi, Chem. Eur. J. 2009, 15, 12770–12779.
E. V. Alexandrov, A. V. Virovets, V. A. Blatov, E. V. Peresypkina,
Chem. Rev. 2015, 115, 12286–12319.
M. A. Lacour, N. J. Rahier, M. Taillefer, Chem. Eur. J. 2011, 17,
12276–12279.
N. Kurono, K. Arai, M. Uemura, T. Ohkuma, Angew. Chem. Int. Ed.
2008, 47, 6643–6646.
[58]
J. A. Lely, J. M. Bijvoet, Recl. des Trav. Chim. des Pays-Bas 2010,
61, 244–252.
M. B. Sassaman, G. K. S. Prakash, G. A. Olah, J. Org. Chem. 1990,
55, 2016–2018.
This article is protected by copyright. All rights reserved.

10.1002/anie.201901173
Angewandte Chemie International Edition
COMMUNICATION
Table of Contents
COMMUNICATION
The dose makes the hexacyanido-
silicates. Treatment of ꢀ[R4N]2[SiF6]
with an excess of Me3Si-CN at 25 ° or
100 °C, respectively, led to the
formation of salts bearing either the
[SiF(CN)5]2– or the [Si(CN)6]2– dianion.
The [Si(CN)6]2– ion was shown to be
utilized for the synthesis of ionic liquids
as well as building block for the design
of coordination polymers, when Lewis
acidic metals are used as counter ions.
Jörg Harloff, Dirk Michalik, Simon Nier,
Axel Schulz,* Philip Stoer, and
Alexander Villinger
Page No. – Page No.
Cyanidosilicates – Synthesis and
Structure
Fuer Mendeley
Ref 53 When a Mixture of water/CH2Cl2 was used as solvent, [Pr3(ClCH2)N][Si(CN)6] was obtained in small yields (see X-Ray data Table S9 and Figure S12),
indicating HCl elimination.
This article is protected by copyright. All rights reserved.