Hexacyanidosilicates with Functionalized Imidazolium Counterions

Article abstract of DOI:10.1002/ejic.202000281

Functionalized imidazolium cations were combined with the hexacyanidosilicate anion, [Si(CN)₆]^2–, by salt metathesis reactions with K₂[Si(CN)₆], yielding novel ionic compounds of the general formula [R–Ph(nBu)Im

Full text of DOI:10.1002/ejic.202000281

European Journal of Inorganic Chemistry
Accepted Article
Title: Hexacyanidosilicates with Functionalized Imidazolium
Counterions
Authors: Jörg Harloff, Karoline Charlotte Laatz, Swantje Lerch, Axel
Schulz, Philip Stoer, Thomas Strassner, and Alexander
Villinger
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000281
Link to VoR: https://doi.org/10.1002/ejic.202000281
01/2020

10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
Hexacyanidosilicates with Functionalized Imidazolium
Counterions
Jörg Harloff,[a] Karoline Charlotte Laatz,[a] Swantje Lerch,[c] Axel Schulz,*[a,b] Philip Stoer,[a] Thomas
Strassner,*[c] Alexander Villinger[a]
[a]
K. C. Laatz, Dr. J. Harloff, P. Stoer, Prof. Dr. A. Schulz, Dr. A. Villinger
Anorganische Chemie, Institut für Chemie
Universität Rostock
18059 Rostock, A.-Einstein-Str. 3a
E-mail: axel.schulz@uni-rostock.de
Prof. Dr. A. Schulz
[b]
[c]
Materialdesign
Leibniz-Institut für Katalyse an der Universität Rostock
18059 Rostock, A.-Einstein-Str. 29a
S. Lerch, Prof. Dr. T. Strassner
Physikalische Organische Chemie
Technische Universität Dresden
01069 Dresden, Bergstraße 66
E-mail: thomas.strassner@chemie.tu-dresden.de
Supporting information and the ORCID numbers of the authors of this article are available on the WWW.
Abstract: Functionalized imidazolium cations were combined with the
hexacyanidosilicate anion, [Si(CN)6]2−, by salt metathesis reactions
with K2[Si(CN)6], yielding novel ionic compounds of the general
formula [R-Ph(nBu)Im]2[Si(CN)6] (R = 2-Me (1), 4-Me (2), 2,4,6-
Me = Mes (3), 2-MeO (4), 2,4-F (5), 4-Br (6); Im = imidazolium). All
synthesized imidazolium hexacyanidosilicates decompose upon
thermal treatment above 95°C (96 – 164 °C). Furthermore, the hexa-
borane-adduct [Mes(nBu)Im]2{Si[(CN)B(C6F5)3]6}·6 CH2Cl2 (7), which
is thermally stable up to 215 °C, was obtained from the reaction of 3
with Lewis acidic B(C6F5)3. In CH3CN solution, decomposition of the
hexaadduct to the Lewis-acid-base adduct CH3CN–B(C6F5)3 and
One class of cations in IL chemistry, which are often used, are
imidazolium cations, as they can easily be substituted at the
nitrogen atoms and / or at the C–H acidic position of the five-
membered ring with linear or branched alkyl chains of different
lengths.[24] So called tunable aryl alkyl ionic liquids (TAAILs) allow
a much greater diversity as they exhibit an alkyl and an aryl moiety
at the heteroatoms of the imidazolium cation. They offer
interesting electronic effects, which can be introduced at the
phenyl ring system by changing type, number and position of the
substituents. The TAAILs are easily accessible by a two-step
synthesis protocol. First, an aniline derivative, glyoxal, form-
aldehyde and an ammonium halide are converted in an one-pot
reaction. In a second step a nucleophilic substitution of the
imidazole leads to the imidazolium halide salt (Scheme 1).[25–27]
[(C6F5)3B·(µ-CN)·B(C6F5)3]− was observed.
All synthesized
compounds were isolated in good yields and were completely
characterized including single crystal structure elucidations.
Introduction
It was Paul Walden in 1914, who synthesized [EtH3N]NO3
(m.p. = 12 °C), one of the first known ionic liquids (IL).[1] Due to
weak Coulomb interactions between organic cations and organic
or inorganic anions, such salts usually possess a low melting point
(< 100 °C) and are also referred to as room temperature ionic
liquids (RTILs) if the melting point is below 25 °C. By combining
cations and anions in a wide variety of ways, or by selectively
modifying organic residues of the ions, physical properties such
as melting point, viscosity, high thermal stability, volatility and
acidity can be influenced, which is why ILs are also called
"designer solvents".[2] Due to these variable properties, ILs have
been extensively investigated in recent years and have been used,
for example, as solvents in organic and catalytic syntheses,[2–5] as
electrolyte liquids in batteries,[6–9] as additives in dye cells,[10–12] as
extraction media for metals[13–15] or for the synthesis of
nanoparticles[16,17] and metal clusters.[18–20] Furthermore, they are
used in processes such as dissolving of cellulose[21] or for the
synthesis of alkoxyphenyl-phosphines in the industrial BASIL™
process.[22,23]
Scheme 1. Syntheses of Tunable Aryl Alkyl Ionic Liquids (TAAILs).
We were interested to synthesize new ionic liquids by combining
the properties of the low-melting TAAILs with the
hexacyanidosilicate dianion, [Si(CN)6]2−. Just recently, we
reported on the successful synthesis of the cyanido(fluorido)-
silicate dianions. Via temperature controlled F− / CN− exchange
reactions of ammonium fluoridosilicates in an excess of neat
Me3Si–CN, we were able to form salts with [SiF(CN)5]2− and
[Si(CN)6]2− as counter anions. A facile neutralization reaction in
water of KOH with protic ammonium salts, such as
[nPr3NH]2[Si(CN)6], enabled access to amorphous, solvent free
potassium hexacyanidosilicate after drying in vacuo.
Crystallization at low temperatures from
a concentrated
1
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10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
acetonitrile solution led to formation of K2[Si(CN)6]·6 CH3CN. In a
subsequent salt metathesis of the solvent free K2[Si(CN)6] with
[BMIm]Br (BMIm = 3-Butyl-1-methylimidazolium), the ionic liquid
[BMIm]2[Si(CN)6] (Tm.p. = 72 °C) was obtained.[28]
Simultaneously to our publication, Portius and co-workers
reported on a further synthesis strategy for the preparation of
[PPN]2[Si(CN)6] ([PPN]+ = Bis(triphenylphosphine)iminium) as
well as on the heavier homologues of germanium and tin
([PPN]2[Ge(CN)6] and [PPN]2[Sn(CN)6]).[29]
Here we report on the solvent free structure of K2[Si(CN)6] and
on the synthesis of different substituted phenyl-n-butyl-
imidazolium hexacyanidosilicate salts. None of these salts can be
classified as IL, since only decomposition of the compounds was
observed at elevated temperatures. Furthermore, we examined
the reaction of [Mes(nBu)Im]2[Si(CN)6] towards the Lewis-acid
B(C6F5)3 that led to the formation of a very bulky hexaadduct.
B(C6F5)3. This Lewis-acid-base reaction was hampered in the
past, since ammonium hexacyanidosilicate salts were only
soluble in polar solvents such as acetonitrile, which itself forms a
Lewis-acid-base adduct with the borane.[30] Therefore,
[Mes(nBu)Im]2[Si(CN)6] was chosen as starting material because
the cation allows the salt to dissolve in non-Lewis basic solvents
such as dichloromethane. Initially, we aimed to synthesize
pentavalent [Si(CN)5]− salts by abstracting a cyanide moiety with
B(C6F5)3 (Scheme 3, route A). Thus, one equivalent of B(C6F5)3
and [Mes(nBu)Im]2[Si(CN)6] were dissolved in dichloromethane.
However, only different substitution patterns of silicate-borane
adducts and remaining hexacyanidosilicate were observed by
means of 13C{1H} and 19F{1H} NMR experiments but no product
species could be isolated from the mixture. Hence, the procedure
was repeated but with an excess (n = 6) of B(C6F5)3 (Scheme 3,
route B). The starting materials were dissolved in
dichloromethane and both solutions were combined afterwards.
The mixture was immediately placed at a non-vibrating location
which led to the formation of small crystals of
[Mes(nBu)Im]2{Si[(CN)·B(C6F5)3]6} · 6 CH2Cl2 (7) within several
minutes in good yields (see Table 1).
Results and Discussion
Synthesis and Properties of [R-Ph(nBu)Im]2[Si(CN)6] (R = 2-
Me (1), 4-Me (2), 2,4,6-Me = Mes (3), 2-MeO (4), 2,4-F (5), 4-Br
(6)) and [Mes(nBu)Im]2{Si[(CN)·B(C6F5)3]6}·6 CH2Cl2 (7)
Table 1. Decomposition temperatures [°C] (heating rate 5 K·min−1) and yields
[%] of all synthesized compounds.
We started this project with the synthesis of K2[Si(CN)6] by
treating [Et3NH]2[Si(CN)6] with two equivalents of KOH in water
(Scheme 2), according to a slightly changed literature known
process mentioned above.[28] The potassium salt was isolated by
fractional crystallization from the mother lye. Single crystals could
be obtained, suitable for X-ray analysis (Figure 1) which revealed
the formation of a solvent-free structure. According to EA, the
water content amounts to approx. 1.4 wt.-% (K2[Si(CN)6]·0.2 H2O).
All following imidazolium hexacyanido-silicates, generalized as
[R-Ph(nBu)Im]2[Si(CN)6] (R = 2-Me (1), 4-Me (2), 2,4,6-Me = Mes
(3), 2-MeO (4), 2,4-F (5), 4-Br (6)) were prepared by facile salt
metathesis reactions of K2[Si(CN)6] with two equivalents of [R-
Ph(nBu)Im]Br in acetonitrile (Scheme 2). The compounds were
purified by filtering off KBr and isolated by crystallization
(specifications in experimental details). Since all obtained
imidazolium salts tend to decompose at elevated temperatures
without melting, none of these salts can be regarded as IL. Yields
and decomposition points are listed in Table 1.
# (R)
Tdec.
164
119
146
125
yield
67
# (R)
5 (F)
6 (Br)
7
Tdec.
96
yield
43
69
/
1 (2-Me)
2 (4-Me)
3 (Mes)
4 (MeO)
55
138
215
230
54
55
8
80
Scheme 3. Reaction of 3 with different equivalents of B(C6F5)3 (n = 1 or 6).
Route A: Assumed synthesis of [Si(CN)5]− and [(NC)B(C6F5)3]− containing salts
(n = 1). Route B: Complete hexa-substitution of [Si(CN)6]2− by B(C6F5)3 (n = 6)
forming the {Si[(CN)·B(C6F5)3]6}2− anion as CH2Cl2 solvate (7) which can be
transferred to the solvent-free form 8 upon drying at elevated temperatures.
Crystals of 7 were investigated by X-ray (Figure 4) and
thermogravimetric analysis (TGA). The compound decomposes
at elevated temperature (Tdec. = 215 °C) and due to TGA
experiments, loss of co-crystallized CH2Cl2 was observed
(Heating rate 5 K·min−1, ESI Figure S41). The solvent-free form 8
(Tdec. = 230 °C) was obtained when 7 was gently dried at 100 °C
under reduced pressure as proven by EA. Furthermore, the salt
was characterized in solution by means of NMR experiments.
Since 8 is only sparingly soluble in dichloromethane-d2, no
13C{1H} / 29Si(IG) NMR signals for the [Si(CN)6] core were
observed. The 11B{1H} NMR resonance for the coordinating
Scheme 2. Synthesis of K2[Si(CN)6] and subsequent formation of imidazolium
hexacyanidosilicates by salt metathesis reactions in acetonitrile.
Besides the synthesis of imidazolium hexacyanidosilicates, we
were also interested in studying the reactivity of the
hexacyanidosilicate anion towards strong Lewis acids such as
2
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10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
B(C6F5)3 moieties was found at –9.9 ppm with a large line width
of Δν1/2 = 1060 Hz. A broad signal shape is a well-known
phenomenon for compounds in which the B(C6F5)3 moieties
coordinate to the nitrogen of the nitriles.[31–33] The effect of
broadening might be further enhanced due to a slowed rotational
reorientation due to the significant size of the anion. With respect
to uncoordinated, naked B(C6F5)3 (59.1 ppm in CD2Cl2),[34] this
signal is considerably shifted to lower frequencies but found in the
expected region as reported for other 4-coordinated
cyanidoborates (Table 2).[34]
different K+ ions (each N atom to two K+ ions), while the slightly
distorted octahedrally surrounded K+ ion is linked to N atoms of
cyanide ligands of six different adjacent [Si(CN)6]2− ions (Figure 1,
top). Main motifs in the crystal structure are planar four-
membered K2N2 assemblies, twelve-membered K2Si2(CN)4
entities in chair conformation, connecting two different [Si(CN)6]2−
ions, and bended eight-membered K2NSi(CN)2 units, building a
3D network (Figure 1, bottom). The Si–C bonds are in the
expected
range
(d(Si–C) = 1.9506(8) Å,
cf.
Σrcov.(Si–
C) = 1.91 Å)[35], while the K···N contacts with 2.836(1) Å are
slightly elongated compared to the sum of the covalent radii (cf.
Σrcov.(K–N) = 2.67 Å)[35] and shortened compared to the K···N
distance in KCN with 3.00 Å.[36]
8 undergoes reaction with acetonitrile which can be observed
nicely with 11B{1H} NMR. At room temperature a broad and low-
field shifted resonance at –11.3 and a sharper signal at −22 ppm
(Δν1/2 = 100 Hz) are observed. When the temperature is
increased, the first resonance can be recognized as
a
superposition of two distinct signals at −11.3 and −12.2 ppm (see
ESI Figure S39). Cleavage of the N–B donor-acceptor bonds of 8
results in formation of the borane-acetonitrile-d3 adduct CD3CN–
B(C6F5)3, which can be assigned to the most low-field shifted
resonance at −11.3 ppm (cf. −10.3 ppm in benzene).[30] The
signals at −12.2 and −22 ppm can be assigned to [(C6F5)3B·(µ-
CN)·B(C6F5)3]−, which is in good accordance with values known
from the literature.[32,33] This means that at least one CN ligand is
abstracted from the [Si(CN)6] scaffold, which could lead to the
formation of [Si(CN)5]− and lower substituted silicon species.
However, no new signals for any of these species could be
observed by means of 13C{1H} and 29Si(IG) NMR and no product
material could be isolated from the reaction mixture so far.
N–B-bond cleavage was also noticed when the sample was
analyzed by (ESI-TOF)-MS due to the reaction with the column
eluent methanol. As a result, new ions were detected with
m/z = 529 and 543 for [B(C6F5)3OH]− and [B(C6F5)3(OMe)]−,
respectively. The Raman spectrum of 8 shows a single sharp
resonance at 2268 cm−1 for the CN vibration. The signal is shifted
to higher wavenumbers with respect to 3 at 2172 cm−1 (strongest),
indicating a strengthening of the CN triple bond. The band is
located in the similar region as for the cyanidoborates mentioned
above (Table 2). However, no band could be detected by means
of IR analysis for CN stretching vibration.
Figure 1. Ball-and-stick representation of the octahedral environment of
[Si(CN)6]2− (top left), K+ (top right) of the molecular ions in the crystal structure
of K2[Si(CN)6. Bottom: view along c-axis of a 2×2×2 cells representation of the
3D network. Selected bond lengths [Å] and angles [°]: Si–C1 1.9506(8), N1ʹʹ–
K1 2.836(1); C1–Si1–C1ʹ 180.0, N1ʹʹ–K1–N1ʹʹʹ 177.57(3), N1ʹʹ–K1–N1ʹv 87.05(3).
Symmetry code: (ʹ) –x+y, –x, 1–z; (ʹʹ) x, x–y, 2–z; (ʹʹʹ) –x+y, –x, 1+z; (ʹv) x, –1+y,
1+z.
All imidazolium hexacyanidosilicates crystallize as block-
shaped and colorless crystals. Only weak anion···cation contacts,
build by C–H···N hydrogen bonds, were found in all structures
according to single crystal X-ray analysis (heavy atom distances,
shortest given d(Ccation···Nanion) [Å]: 6 3.151(4) ≈ 4 3.161(3) ≈ 3
3.173(2) < 5 3.199(3) < 1 3.291(2) < 2 3.331(2) Å). No
cation···cation contacts were found in the imidazolium salt 1, 2
and 6, therefore no coordination polymer in the crystal was
recognized. Interestingly, only in the structures of compound 3
and 4, π-π-stacking of the substituted phenyl rings of the
imidazolium cations in adjacent planes can be observed. In 3 a
parallel-displaced and in 4 a sandwich conformation is found with
centroid-to-centroid distances of 4.2929(5) Å and 3.7882(4) Å,
respectively. These interactions lead to a wave-shaped pattern in
3 or to a step-shaped arrangement in 4 of the cations in the crystal
structure (Figure 2).
Table 2Selected bond lengths [Å], 11B{1H} NMR [ppm] and Raman [cm−1
]
spectroscopic data of 3 and 7 along with reference materials [dca_2B]a,
[tcm_3B]b and [tcb_4B]c as [EMIm]+ (1-Ethyl-3-methylimidazolium) salt.
3
7
[dca_2B]d [tcm_3B]d [tcb_4B]d
11B{1H}
-
−9.9e
2268
−11.8f
−10.1f
−8.5f
Raman
CN
2164
2172g
2365
2297g
2353
2323
d(C–N)h
1.151(2) 1.136(8)
1.135(6)
1.138(3)
1.136(2)
[a] [N(CN·B(C6F5)3)2]−. [b] [C(CN·B(C6F5)3)3]−. [c] [B(CN·B(C6F5)3)4]−. [d] from
Reference[34]. [e] in CD2Cl2. [f] in CDCl3. [g] most intense. [h] average.
In the 2,4-difluoro-substituted compound 5, a layered motif
(ABAB) is formed in the crystal structure, stabilized by C–H···F
hydrogen bonds which are formed between adjacent imidazolium
cations (Figure 3). The para-F atoms are exclusively connected
to a imidazolium ring in the same layer (e: d(p-F–C) = 3.106(3) Å),
while the ortho-F atoms are linked to a butyl chain (c: d(o-F–
C) = 3.329(3) Å) of an adjacent imidazolium cation in the same
Structure Elucidation
The colorless, block-shaped crystals of solvent-free K2[Si(CN)6]
crystallizes isotypically to known Li2[Si(CN)6] · 2 H2O[28] in the
trigonal space group P3m1 with one formula unit per cell, shown
in Figure 1. The octahedral [Si(CN)6]2− ion coordinates to twelve
̅
3
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10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
layer and also to the C–H-acidic position of a cation in a second
one (d: d(o-F–C) = 3.251(2) Å).
(Table 2). The cyanide ligands are slightly bent away from the Si
center with ∡(Si–C–N) = 173.3(6)°, 172.3(6)°, 175.2(5)° (cf.
178.1(1)° (average) in 3), probably due to the steric stress and the
electrostatic repulsion of the F atoms between the bulky B(C6F5)3
molecules (d(F···F) = 2.78(1) Å (shortest)). Weak anion···cation
interactions can be considered, formed by C–H···F hydrogen
bonds between the anion and different H atoms of the
[Mes(nBu)Im]+ ion (non-hydrogen atom distances and only A-
layer of the disorder is discussed: (F···Calkyl): 3.24(2), 3.27(3),
3.39(2); (F···CMes): 3.09(2), 3.28(3); (F···CIm): 3.00(2) Å).
Figure 2. Wires-and-sticks representations of a section of the crystal structures
of 3 (left) and 4 (right). The [Si(CN)6]2− ions are omitted for reasons of clarity.
View along the a-axis (both). Selected centroid-to-centroid distances [Å]:
a = 4.2929(5), b = 3.7882(4).
Figure 4. Molecular structure of the {Si[(CN)B(C6F5)3]6}2− anion in the crystal
structure of 7. The [Si(CN)6]-core is represented as ball-and-stick model, while
the B(C6F5)3 molecules are shown as wires-and-sticks model. The
[Mes(nBu)Im]+ cations, as well as disorders are omitted for reasons of clarity.
Selected bond lengths [Å] and angles [°]: Si–C1 1.958(6), Si–C2 1.945(6), Si–
C1 1.957(7), C1–N1 1.138(7), C2–N2 1.137(8), C3–N3 1.131(9), N1–B1
1.608(8), N2–B2 1.589(9), N3–B3 1.597(9); Si–C1–N1 172.3(6), Si–C2–N2
173.3 (6), Si–C3–N3 175.2(5), C1–Si–C1ʹ 180.0, C1–Si–C2ʹ 90.1(3). Symmetry
code: (ʹ) 1−x, 1−y, 1−z.
Conclusion
In conclusion, we present facile salt metathesis reactions of
K2[Si(CN)6] with different substituted imidazolium bromides of the
type [R-Ph(nBu)Im]Br, leading to imidazolium hexacyanido-
silicate salts in moderate yields (43 – 69 %), which decompose at
elevated temperatures and thus cannot be regarded as ILs. X-ray
structure elucidation of the solvent-free K2[Si(CN)6] revealed the
formation of a 3D network. The crystal structures of the
imidazolium hexacyanidosilicates show depending on the
substituents either well-separated molecular ions (1, 2 and 6) or
have structural motifs like a wave-shaped (3) or stepped (4)
arrangement due to π-π interactions of the phenyl system. In case
of 5 the cations are arranged in ABAB layers, stabilized by
intermolecular F···H hydrogen bridges. The reaction of the Lewis
acidic borane B(C6F5)3 with the [Si(CN)6]2− dianion led to complete
functionalization of the cyanide ligands and the voluminous
{Si[(CN)B(C6F5)3]6}2− anion in form of its [Mes(nBu)Im]+ salt was
obtained. The compound is only sparingly soluble in CH2Cl2 and
readily decomposes under N–B bond cleavage when polar
solvents such as CH3CN or MeOH are used. This new anion could
possibly be used as a very bulky, weakly coordinating anion when
it is combined with transition metals and could increase its
catalytic activity due to reduced ion pairing.
Figure 3. Wires-and-sticks representations of a section of the crystal structures
of 5. View along a-axis (left) and b-axis (right). The [Si(CN)6]2− ions are omitted
for clarity. Selected distances in Å, heavy-atom distance in the H-bridges: c F1–
C16 3.329(3), d F1–C4 3.251(2), e F2–C6 3.106(3).
[Mes(nBu)Im]2{Si[(CN)B(C6F5)3]6}∙6 CH2Cl2 (7) crystallizes in
̅
the triclinic space group P1 with one formula unit per cell. The
octahedral [Si(CN)6] core links via the N atoms to six B(C6F5)3
molecules, forming a bulky, spherical anion (Figure 4). Due to the
poor quality of the data (wR2 = 33 %), we would like to point out
that a discussion regarding to structural parameter such as bond
length and angles should be handled with care. However, the N–
B donor-acceptor bonds are in the range of a covalent single bond
(d(N–B) = 1.598(1) Å (average), cf. Σrcov.(N–B) = 1.56 Å)[35] and of
similar strength compared to the N–B bond(s) in CH3CN–B(C6F5)3
with 1.616(3) Å,[30] HCN–B(C6F5)3 with 1.606(3) Å[37] or in
{B[(CN)·B(C6F5)3]4}− with 1.606(2) Å (average),[34] as the
structural data clearly demonstrate. The C–N triple bond with
1.136(8) Å (average) is shortened compared to the C–N distance
in 3 that nicely correlates to observations of Raman analyses
4
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10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
used. The product was crystallized from a mixture of acetonitrile and
CH2Cl2 at −30 °C leading to formation of colorless crystals in yields of 67 %
(1.4 g, 2.2 mmol). Tdec. = 164 °C. EA % calc. (found) %: C 66.42 (65.51);
Experimental Section
Caution! TMS–CN is highly toxic! Appropriate safety precautions (HCN
detector, gas mask, low temperature) should be taken. Experimental
spectra and additional crystal structure representations can be found in the
Supporting Information.
H
6.23 (5.81); N 22.78 (22.24). (ESI)-MS (m/z) pos.: 215 ([2-
MePh(nBu)Im]+); neg.: 106 ([Si(CN)3]−); 158 ([Si(CN)5]−). 1H NMR (300 K,
CD3CN, 250.13 MHz): δ = 0.99 (t, 6H, CH2CH3, 3J(1H–1H) = 7.3 Hz),
1.33 – 1.51 (m, 4H, CH2CH3), 1.92 – 2.01 (m, 4H, CH2CH2), 2.23 (s, 6H,
Ph-CH3), 4.28 (t, 4H, NCH2, 3J(1H–1H) = 7.3 Hz), 7.38 – 7.55 (m, 8H, CAryl),
7.55 – 7.60 (m, 2H, NCHCHN–nBu), 7.62 – 7.67 (m, 2H, NCHCHN–nBu),
8.67–8.71 (m, 2H, NCHN). 13C{1H} NMR (300 K, CD3CN, 62.9 MHz): δ =
13.7 (s, CH2CH3), 17.5 (s, o-CH3), 20.1 (s, CH2CH3), 32.4 (s, CH2CH2),
50.8 (s, NCH2), 123.7 (s, NCHCHN–nBu), 125.0 (s, NCHCHN–nBu), 127.5
(s, CAryl), 128.4 (s, CAryl), 132.0 (s, CAryl), 132.7 (s, CAryl), 134.9 (s, ipso-
CN), 135.2 (s, CAryl), 137.0 (s, NCHN), 140.0 (s, Si(CN)6). 29Si(IG) NMR
(300 K, CD3CN, 99.3 MHz) not observed (Si(CN)6). IR (ATR, 298 K, 32
General Information: All manipulations were carried out in oxygen- and
moisture-free conditions in an argon atmosphere using standard Schlenk
or dry-box techniques if not mentioned otherwise.
NMR spectra were recorded on Bruker spectrometers (AVANCE 250,
AVANCE 300 or AVANCE 500) and were referenced internally to the
deuterated solvent (13C: CD2Cl2 δref = 54.0 ppm, CD3CN δref,1 = 1.3 ppm,
δref,2 = 118.3 ppm), to protic impurities in the deuterated solvent (1H:
CHDCl2 δref = 5.32 ppm, CHD2CN δref = 1.94 ppm,)[38] or externally (19F:
CFCl3 δref = 0 ppm, 29Si: SiMe4 δref = 0 ppm). All measurements were
carried out at ambient temperature unless denoted otherwise. IR spectra
were recorded with a Bruker Alpha II FT-IR spectrometer with ATR device.
For Raman spectroscopy a LabRAM HR 800 Horiba Jobin YVON
equipped with an Olympus BX41 microscope with variable lenses were
used. The samples were excited by a red laser (633 nm, 17 mW, air-
cooled HeNe laser), a green laser (532 nm, 50 mW, air-cooled, frequency-
doubled Nd:YAG solid-state laser) or a blue laser (473 nm, 20 mW, air-
cooled solid-state laser). All measurements were carried out at ambient
temperature unless stated otherwise. CHN analyses were recorded using
an Elementar vario Micro cube CHNS analyser. For TGA, samples were
analyzed using a Setaram Instrumentation Labsys analyzer. Melting points
(uncorrected) were measured with a Stanford Research Systems (heating
rate 5 K·min−1 (clearing-points are reported)). Mass spectra were recorded
with a Xevo G2-XS TOF system coupled with a LC from Waters or with an
Agilent Technologies 6130 Quadrupole system coupled with a LC from
Agilent Technologies 1260 Infinity system.
scans, cm–1): ν =420(w), 441(w), 451(w), 464(w), 569(vs), 624(vw), 637(vw),
̃
655(w), 678(vw), 717(w), 750(w), 762 (m), 775(w), 800(vw), 824(vw), 859(w),
884(vw), 958(vw), 1026(vw), 1047(vw), 1076(w), 1121(w), 1191(m), 1212(w),
1249 (vw), 1271 (vw), 1300 (vw), 1337 (vw), 1368 (vw), 1381 (vw), 1391 (vw),
1416 (vw), 1449 (w), 1461 (w), 1494 (w), 1554 (w), 1568 (w), 1636 (vw), 1655
(vw), 1714 (vw), 2166 (vw), 2875 (vw), 2932 (vw), 2961 (w), 3093 (w), 3118 (vw),
3126 (vw), 3140 (w). Raman (laser: 633 nm, accumulation time: 4 s, 16
scans, 298 K, cm–1): ν =71(4), 80(6), 105(6), 145(6), 194(1), 277(1), 306(1),
̃
322 (1), 369 (0), 406 (1), 453 (1), 468 (2), 549 (2), 554 (2), 627 (1), 656 (1), 659
(1), 682 (1), 718 (1), 752 (1), 801 (2), 825 (1), 885 (1), 962 (3), 999 (1), 1028 (1),
1046(2), 1078(1), 1120(1), 1161(1), 1212(1), 1250(1), 1274(1), 1307(1), 1338
(1), 1359 (1), 1372 (2), 1391 (1), 1419 (2), 1436 (1), 1448 (1), 1464 (1), 1497 (1),
1556 (1), 1585 (1), 1610 (1), 2118 (1), 2164 (3), 2171 (10), 2735 (1), 2875 (2),
2915(2), 2933(3), 2966(3), 2989(1), 3009(1), 3068(2), 3081(2), 3130(2), 3158
(1).
[4-MePh(nBu)Im]2[Si(CN)6] (2): 0.5 g (1.9 mmol) of the potassium
hexacyanidosilicate and 1.8 g (3.8 mmol, 2 eq.) of [4-MePh(nBu)Im]Br was
used. The product was crystallized from CH2Cl2 leading to formation of
colorless crystals in yields of 55 % (0.7 g, 1.1 mmol). Tdec. = 119 °C. EA %
calc. (found) %: C 66.42 (66.19); H 6.23 (6.23); N 22.78 (22.65). (ESI)-MS
(m/z) pos.: 215 ([4-MePh(nBu)Im]+); neg.: 106 ([Si(CN)3]−); 158
([Si(CN)5]−). 1H NMR (300 K, CD3CN, 300.13 MHz): δ = 0.98 (t, 6H,
CH2CH3, 3J(1H–1H) = 7.4 Hz), 1.35 – 1.48 (m, 4H, CH2CH3), 1.87 – 2.00
(m, 4H, CH2CH2), 2.43 (s, 6H, ph-CH3), 4.26 (t, 4H, NCH2, 3J(1H–1H) = 7.4
Hz), 7.40 – 7.47 (m, 4H, m-CH), 7.41 – 7.55 (m, 4H, o-CH), 7.59 – 7.60 (m,
2H, NCHCHN–nBu), 7.74 – 7.75 (m, 2H, NCHCHN–nBu), 8.98 – 9.03 (m,
2H, NCHN). 13C{1H} NMR (300 K, CD3CN, 75.5 MHz): δ = 13.7 (s,
CH2CH3), 20.0 (s, CH2CH3), 21.1 (s, Ph-CH3), 32.4 (s, CH2CH2), 50.8 (s,
NCH2), 122.7 (s, NCHCHN–nBu), 123.2 (s, m-CH) 124.1 (s, NCHCHN–
nBu), 131.7 (s, o-CH), 133.5 (s, ipso-CN), 135.4 (s, NCHN), 140.0 (s,
Si(CN)6) 141.7 (s, ipso-Cpara). 29Si(IG) NMR(300 K, CD3CN, 99.3 MHz) not
X-ray Structure Determination: X-Ray quality crystals of all compounds
were selected in Kel-F-oil (Riedel de Haen) at ambient temperatures.
Single crystals were measured on a Bruker D8 Quest or a Bruker Apex
Kappa II CCD diffractometer using graphite-monochromated Mo Kα
radiation (λ= 0.71073). The structures were solved by iterative methods
(SHELXT)[39] and refined by full-matrix least squares procedures
(SHELXL)[40]
.
Semi-empirical absorption corrections were applied
(SADABS)[41]. All non-hydrogen atoms were refined anisotropically and
hydrogen atoms were included in the refinement at calculated positions
using a riding model.
CCDC 1984754 – 1984761 contain the supplementary crystallographic
data for this paper. All data can be obtained free of charge via
observed (Si(CN)6). IR (ATR, 298 K, 32 scans, cm–1): ν = 422 (w), 437 (w),
̃
www.ccdc.cam.ac.uk/data_request/cif,
or
by
emailing
464 (w), 530 (s), 569 (vs), 639 (w), 657 (w), 705 (vw), 721 (vw), 742 (w),
773 (m), 800 (vw), 816 (m), 830 (w), 857 (w), 884 (vw), 907 (vw), 958 (vw),
1020 (vw), 1047 (vw), 1078 (w), 1117 (w), 1125 (vw), 1205 (m), 1236 (vw),
1271 (vw), 1300 (vw), 1333 (vw), 1381 (w), 1414 (vw), 1459 (w), 1471 (w),
1510 (w), 1556 (w), 1568 (w), 1638 (vw), 1651 (vw), 1710 (vw), 1904 (vw),
2164 (vw), 2875 (w), 2932 (w), 2955 (w), 2965 (vw), 3097 (w), 3118 (vw),
3142 (w). Raman (laser: 633 nm, accumulation time: 4 s, 20 scans, 298 K,
data_request@ccdc.cam.ac.uk or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033.
Compound Syntheses
cm−1): ν = 80 (5), 89 (5), 143 (4), 237 (1), 270 (1), 292 (1), 302 (1), 326 (1),
̃
Bromide salts [R-Ph(nBu)Im]Br with R = 2-Me, 4-Me, 2,4,6-Me and 2-MeO
were prepared according to the literature.[25–27,42] The synthesis of the
starting compounds K2[Si(CN)6], [2,4-FPh(nBu)Im]Br and [4-
BrPh(nBu)Im]Br can be found in the supporting information.
341 (1), 361 (1), 385 (1), 406 (1), 467 (2), 531 (1), 607 (1), 629 (1), 640(1),
658 (1), 706 (1), 722 (1), 775 (1), 800 (3), 818 (1), 831 (1), 859 (1), 908
(1), 959 (5), 1009 (1), 1021 (1), 1033 (1), 1079 (1), 1117 (1), 1183 (2),
1206 (1), 1218 (1), 1265 (1), 1272 (1), 1302 (1), 1309 (1), 1334 (1), 1370
(1), 1380 (1), 1414 (2), 1446 (1), 1463 (1), 1473 (1), 1513 (1), 1558 (1),
1571 (1), 1612 (1), 2117 (1), 2123 (1), 2164 (2), 2171 (10), 2742 (1), 2873
(1), 2929 (1), 2949 (1), 2964 (1), 2990 (1), 3017 (1), 3046 (1), 3075 (2),
3130 (1), 3155 (1).
General Synthesis of Imidazolium Hexacyanidosilicates (1 – 6):
K2[Si(CN)6] (1 eq.) and [R-Ph(nBu)Im]Br (2 eq.) were placed in a Schlenk-
flask. The solids were suspended in 50 mL of acetonitrile and stirred for 16
hours at room temperature. The suspension was filtered with a glass frit
and acetonitrile was removed in vacuo.
[Mes(nBu)Im]2[Si(CN)6] (3): 0.8 g (3.0 mmol) of the potassium
hexacyanidosilicate and 1.9 g (6.1 mmol, 2 eq.) of [Mes(nBu)Im]Br was
used. The product was crystallized from a mixture of diethyl ether and
CH2Cl2 at −30 °C leading to formation of colorless crystals in yields of 54 %
[2-MePh(nBu)Im]2[Si(CN)6] (1): 0.9
hexacyanidosilicate and 1.9 g (6.8 mmol, 2 eq.) of [2-MePh(nBu)Im]Br was
g (3.4 mmol) of potassium
5
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
(1.1 g, 1.6 mmol). Tdec. = 146 °C. EA % calc. (found) %: C 68.03 (68.37);
H 6.91 (7.54); N 20.88 (20.75). (ESI)-MS (m/z) pos.: 243 ([Mes(nBu)Im]+);
neg.: 106 ([Si(CN)3]−); 158 ([Si(CN)5]−). 1H NMR (298.5 K, CD3CN, 300.13
MHz): δ = 0.98 (t, 6H, CH2CH3, 3J(1H–1H) = 7.2 Hz), 1.32 – 1.44 (m, 4H,
CH2CH3), 1.94 – 1.98 (m, 4H, CH2CH2), 2.04 (s, 12H, o-CH3), 2.36 (s, 6H,
p-CH3), 4.27 – 4.32 (m, 4H, NCH2), 7.12 (s, 4H, m-CH), 7.44 – 7.47 (m,
2H, NCHCHN–nBu), 7.66 – 7.69 (m, 2H, NCHCHN–nBu), 8.60 – 8.66 (m,
2H, NCHN). 13C{1H} NMR (298.5 K, CD3CN, 75.5 MHz): δ = 13.7 (s,
CH2CH3), 17.4 (s, o-CH3), 20.0 (s, CH2CH3), 21.1 (s, p-CH3), 32.2 (s,
CH2CH2), 50.9 (s, NCH2), 124.2 (s, NCHCHN–nBu), 125.1 (s, NCHCHN–
nBu) 130.4 (s, ipso-Cortho), 132.0 (s, ipso-Cpara), 135.7 (s, m-CH), 137.2 (s,
NCHN), 140.0 (s, Si(CN)6) 142.2 (s, ipso-CN). 29Si(IG) NMR (300 K,
7.72 – 7.78 (m, 2H, o-CH), 8.88 – 8.97 (m, 2H, NCHN). 13C{1H} NMR
(298.1 K, CD3CN, 75.5 MHz): δ = 13.7 (s, CH2CH3), 20.0 (s, CH2CH3), 32.3
(s, CH2CH2), 51.0 (s, NCH2), 106.7 (dd, FCCHCF, 2J(13C–19F) = 24 Hz,
2J(13C–19F) = 28 Hz), 113.9 (dd, m-CH, 2J(13C–19F) = 4 Hz, 4J(13C–19F) =
23 Hz), 120.6 (dd, ipso-CN, 2J(13C–19F) = 4 Hz, 2J(13C–19F) = 11 Hz), 124.0
(s, NCHCHN–nBu), 124.6 (s, NCHCHN–nBu), 129.2 (d, o-CH, 3J(13C–19F)
= 11 Hz), 137.4 (br, NCHN), 140.1 (s, Si(CN)6), 156.8 (dd, o-CF, 3J(13C–
19F) = 13 Hz, 1J(13C–19F) = 254 Hz), 164.5 (dd, p-CF, 3J(13C–19F) = 12 Hz,
1J(13C–19F) = 252 Hz).19F{1H} NMR (298.1 K, CD3CN, 282.37 MHz) δ =
−120.5 (d, 1F, CF, 4J(19F–19F) = 9 Hz), −106.8 (d, 1F, CF, 4J(19F–19F) = 9
Hz). 29Si(IG) NMR (300 K, CD3CN, 99.3 MHz) not observed (Si(CN)6). IR
(ATR, 298 K, 32 scans, cm–1): ν = 429 (m), 482 (m), 509 (m), 571 (vs), 604
̃
CD3CN, 99.3 MHz) not observed (Si(CN)6). IR (ATR, 298 K, 32 scans, cm–
(w), 616 (w), 628 (w), 653 (w), 707 (vw), 721 (vw), 738 (w), 777 (m), 802
(vw), 822 (m), 843 (m), 851 (m), 907 (vw), 944 (w), 975 (m), 1014 (vw),
1032 (vw), 1074 (m), 1105 (m), 1121 (w), 1142 (m), 1185 (m), 1195 (m),
1218 (w), 1236 (w), 1271 (m), 1298 (vw), 1348 (w), 1366 (vw), 1383 (w),
1445 (w), 1461 (w), 1506 (m), 1558 (m), 1572 (w), 1611 (w), 1618 (w),
2172 (vw), 2866 (vw), 2879 (vw), 2938 (w), 2965 (w), 3079 (vw), 3112 (w),
3136 (w), 3149 (w). Raman (laser: 473 nm, accumulation time: 4 s, 13
1
̃
): ν = 431 (m), 569 (vs), 641 (w), 672 (m), 732 (w), 754 (m), 818 (vw), 849
(w), 861 (w), 894 (vw), 936 (vw), 968 (vw), 1018 (vw), 1039 (w), 1067 (w),
1088 (w), 1119 (vw), 1158 (w), 1203 (w), 1292 (vw), 1329 (vw), 1381 (w),
1442 (w), 1461 (w), 1484 (w), 1548 (w), 1566 (w), 1609 (w), 2168 (vw),
2862 (w), 2875 (vw), 2934 (w), 2959 (w), 3093 (vw), 3142 (w), 3165 (vw).
Raman (laser: 633 nm, accumulation time: 12 s, 25 scans, 298 K, cm–1): ν
̃
scans, 298 K, cm–1): ν = 162 (2), 247 (3), 270 (2), 319 (2), 355 (3), 414 (3),
̃
= 96 (10), 148 (4), 235 (2), 320 (2), 335 (2), 352 (1), 408 (2), 445 (1), 467
(2), 501 (1), 512 (1), 556 (1), 577 (4), 821 (1), 893 (1), 946 (1), 970 (3),
1020 (1), 1059 (1), 1070 (1), 1090 (2), 1263 (1), 1297 (1), 1331 (2), 1364
(2), 1374 (2), 1380 (2), 1415 (3), 1442 (2), 1551 (2), 1568 (1), 1611 (2),
2120 (2), 2164 (5), 2172 (10), 2736 (2), 2865 (3), 2878 (3), 2924 (5), 2941
(4), 2957 (3), 2968 (3), 2971 (3), 2976 (3), 2999 (3), 3007 (3), 3010 (3),
3014 (3), 3022 (3), 3026 (3), 3033 (3), 3077 (2), 3080 (2), 3083 (2), 3113
(2), 3117 (2), 3146 (3), 3149 (3), 3168 (3).
431 (3), 467 (3), 569 (3), 742 (5), 947 (4), 977 (5), 1032 (4), 1074 (4), 1119
(4), 1274 (4), 1348 (5), 1367 (6), 1415 (6), 1511 (5), 1561 (5), 1619 (6),
2173 (9), 2179 (10), 2880 (8), 2904 (8), 2925 (8), 2942 (8), 2967 (8), 2973
(8), 2986 (8), 3092 (9), 3111 (8), 3132 (7), 3138 (7), 3149 (7), 3160 (8).
[4-BrPh(nBu)Im]2[Si(CN)6] (6): 0.7 g (2.7 mmol) of potassium
hexacyanidosilicate and 1.9 g (5.4 mmol, 2 eq.) of [4-BrPh(nBu)Im]Br was
used. The product was crystallized from a mixture of acetonitrile and
CH2Cl2 at −30 °C leading to formation of colorless crystals in yields of 69 %
(1.4 g, 1.8 mmol). Tdec. = 138 °C. EA % calc. (found) %: C 51.62 (51.18);
[2-MeOPh(nBu)Im]2[Si(CN)6] (4): 0.5 g (1.9 mmol) of potassium
hexacyanidosilicate and 1.2 g (3.9 mmol, 2 eq.) of [2-MeOPh(nBu)Im]Br
was used. The product was crystallized from CH2Cl2 at room temperature
leading to formation of colorless crystals in yields of 55 % (0.7 g, 1.1 mmol).
Tdec. = 125 °C. EA % calc. (found) %: C 63.13 (62.75); H 5.92 (6.37); N
21.65 (21.39). (ESI)-MS(m/z) pos.: 231 ([2MeOPh(nBu)Im]+); neg.: 106
([Si(CN)3]−); 158 ([Si(CN)5]−). 1H NMR (300 K, CD3CN, 250.13 MHz): δ =
1.00 (t, 6H, CH2CH3, 3J(1H–1H) = 7.4 Hz), 1.34 – 1.52 (m, 4H, CH2CH3),
1.95 – 2.00 (m, 4H, CH2CH2), 3.94 (s, 6H, OCH3), 4.30 (t, 4H, NCH2,
3J(1H–1H) = 7.3 Hz), 7.14 – 7.36 (m, 4H, CHAryl), 7.48 – 7.65 (m, 4H,
CHAryl), 7.59 – 7.62 (m, 2H, NCHCHN–nBu), 7.66 – 7.71 (m, 2H,
NCHCHN–nBu), 8.84 – 8.91 (m, 2H, NCHN). 13C{1H} NMR (300 K, CD3CN,
75.5 MHz): δ = 13.7 (s, CH2CH3), 20.0 (s, CH2CH3), 32.4 (s, CH2CH2), 50.8
(s, NCH2), 57.1 (s, OCH3), 114.1 (s, CAryl), 122.2 (s, CAryl), 123.1 (s, CAryl),
124.5 (s, ipso-CN), 124.6 (s, NCHCHN–nBu), 126.7 (s, CAryl), 132.8 (s,
NCHCHN–nBu), 137.3 (s, NCHN), 140.0 (s, Si(CN)6), 153.4 (s, COCH3).
29Si(IG) NMR (300 K, CD3CN, 99.3 MHz) not observed (Si(CN)6). IR (ATR,
H
4.33 (3.98); N 18.81 (18.34). (ESI)-MS (m/z) pos.: 279 ([4-
BrPh(nBu)Im]+); neg.: 106 ([Si(CN)3]−); 158 ([Si(CN)5]−). 1H NMR (300 K,
CD3CN, 250.13 MHz): δ = 1.00 (t, 6H, CH2CH3, 3J(1H–1H) = 7.3 Hz),
1.34 – 1.55 (m, 4H, CH2CH3), 1.95 – 2.05 (m, 4H, CH2CH2), 4.29 (t, 4H,
NCH2, 3J(1H–1H) = 7.4 Hz), 7.55 – 7.62 (m, 4H, m-CH), 7.62 – 7.68 (m, 2H,
NCHCHN–nBu), 7.76 – 7.82 (m, 4H, o-CH), 7.83 – 7.88 (m, 2H,
NCHCHN–nBu), 8.99 – 9.12 (m, 2H, NCHN). 13C{1H} NMR (300 K, CD3CN,
75.5 MHz): δ = 13.7 (s, CH2CH3), 20.0 (s, CH2CH3), 32.4 (s, CH2CH2), 51.0
(s, NCH2), 122.7 (s, NCHCHN–nBu), 124.4 (s, NCHCHN–nBu), 124.4 (s,
ipso-C–Br), 125.4 (s, CAryl), 134.3 (s, ipso-CN), 135.2 (s, CAryl), 135.7 (s,
NCHN), 140.0 (s, Si(CN)6). 29Si(IG) NMR (300 K, CD3CN, 99.3 MHz) not
observed (Si(CN)6). IR (ATR, 298 K, 32 scans, cm–1): ν = 422 (w), 435 (w),
̃
455 (w), 470 (w), 519 (s), 567 (vs), 633 (w), 647 (w), 703 (w), 750 (m), 789
(vw), 826 (m), 857 (w), 956 (w), 975 (vw), 1010 (w), 1045 (w), 1065 (m),
1100 (vw), 1121 (vw), 1131 (vw), 1195 (m), 1212 (w), 1255 (vw), 1282 (vw),
1294 (vw), 1319 (vw), 1331 (w), 1370 (w), 1389 (vw), 1412 (w), 1424 (w),
1436 (vw), 1459 (w), 1490 (m), 1548 (m), 1564 (w), 1607 (w), 1900 (vw),
2170 (vw), 2357 (vw), 2862 (vw), 2928 (w), 2967 (w), 3077 (w), 3097 (w),
3142 (w), 3165 (vw). Raman (laser: 633 nm, accumulation time: 4 s, 25
198 K, 32 scans, cm–1): ν = 424 (m), 476 (w), 530 (m), 567 (vs), 628 (w),
̃
651 (w), 668 (w), 723 (w), 754 (m), 769 (m), 791 (w), 861 (w), 958 (w), 979
(vw), 1020 (m), 1047 (vw), 1065 (w), 1107 (w), 1125 (w), 1162 (w), 1185
(m), 1197 (w), 1257 (m), 1286 (w), 1302 (w), 1335 (w), 1379 (w), 1422
(vw), 1440 (w), 1461 (w), 1471 (w), 1502 (m), 1554 (w), 1566 (w), 1605
(w), 1933 (vw), 2166 (vw), 2359 (vw), 2846 (vw), 2862 (vw), 2879 (vw),
2941 (w), 2963 (w), 3107 (w), 3140 (w), 3151 (w). Raman (laser: 532 nm,
scans, 298 K, cm–1): ν = 78 (5), 96 (7), 125 (6), 223 (1), 242 (1), 272 (0),
̃
314 (1), 324 (1), 376 (1), 408 (1), 464 (2), 522 (1), 621 (1), 631 (1), 648
(1), 701 (1), 729 (2), 750 (1), 758 (1), 818 (1), 857 (1), 880 (1), 956 (4),
974 (1), 1011 (1), 1024 (1), 1065 (1), 1076 (2), 1099 (1), 1131 (1), 1185
(1), 1196 (1), 1254 (1), 1301 (1), 1330 (1), 1340 (1), 1349 (1), 1360 (4),
1388 (1), 1410 (1), 1425 (4), 1437 (2), 1457 (1), 1491 (1), 1550 (1), 1563
(1), 1591 (4), 2122 (1), 2162 (1), 2172 (10), 2862 (1), 2878 (1), 2899 (1),
2913 (1), 2919 (1), 2922 (1), 2929 (1), 2940 (1), 2964 (1), 3066 (1), 3076
(1), 3117 (1), 3141 (1), 3167 (1).
accumulation time: 3 s, 13 scans, 298 K, cm–1): ν = 129 (4), 346 (1), 411
̃
(1), 465 (2), 794 (4), 885 (4), 959 (4), 985 (4), 1024 (5), 1047 (5), 1163 (5),
1261 (6), 1336 (6), 1361 (6), 1383 (6), 1423 (7), 1461 (7), 1500 (6), 1553
(7), 1595 (8), 2055 (7), 2163 (8), 2167 (8), 2176 (10), 2511 (7), 2851 (6),
2939 (6), 2961 (6), 3087 (6), 3163 (6).
[2,4-FPh(nBu)Im]2[Si(CN)6] (5): .8 g (2.9 mmol) of potassium
hexacyanidosilicate and 1.9 g (5.9 mmol, 2 eq.) of [2,4-FPh(nBu)Im]Br
was used. The product was crystallized from acetonitrile at room
temperature leading to formation of colorless crystals in yields of 43 %
(0.8 g, 1.3 mmol). Tdec. = 96 °C. EA % calc. (found) %: C 58.35 (57.46); H
4.59 (4.73); N 21.26 (20.77). (ESI)-MS (m/z) pos.: 237 ([2,4Ph(nBu)Im]+);
neg.: 106 ([Si(CN)3]−); 158 ([Si(CN)5]−). 1H NMR (298.1 K, CD3CN,
300.13 MHz): δ = 1.00 (t, 6H, CH2CH3, 3J(1H–1H) = 7.5 Hz), 1.39 – 1.47 (m,
4H, CH2CH3), 1.95 – 2.00 (m, 4H, CH2CH2), 4.31 (t, 4H, NCH2, 3J(1H–1H)
= 7.3 Hz), 7.24 – 7.30 (m, 2H, m-CH), 7.31 – 7.37 (m, 2H, CFCHCF),
7.65 – 7.68 (m, 2H, NCHCHN–nBu), 7.70 – 7.72 (m, 2H, NCHCHN–nBu),
[Mes(nBu)Im]2{Si[(CN)B(C6F5)3]6} (8): 0.07 g (0.10 mmol) of
3 is
dissolved in 7 mL of dichloromethane. 0.37 g (0.73 mmol, 7 eq.) of
B(C6F5)3 is dissolved in 8 mL of dichloromethane and added to the silicate
solution with a syringe. Stirring the mixture at room temperature for one
hour leads to formation of a white precipitate which is filtered off and
washed three times with 5 mL of n-hexane to remove excess of B(C6F5)3.
Crystals
of
the
dichloromethane
hexasolvate
[Mes(nBu)Im]2{Si[(CN)·B(C6F5)3]6}·6 CH2Cl2 (7) can be obtained by
recrystallization from hot dichloromethane. Drying the crystals at 100 °C in
vacuo leads to 0.30 g (0.08 mmol) of colorless and solvate-free product (8)
6
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10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
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in yields of 80 %. Note: Crystals of 7·can be obtained when combining a
dichloromethane solution of both starting materials and placing the mixture
at a vibration-free place. Tdec = 230 °C (8), Tdec = 215 °C (7). EA % calc.
(found) %: C 46.85 (47.15); H 1.24 (1.05); N 3.74 (3.79). (ESI)-MS (m/z)
pos.: 243 ([Mes(nBu)Im]+); neg.: n.o. ([anion]−)*; 528 ([(HO)B(C6F5)3]−)*;
543 ([(MeO)B(C6F5)3]−)*. 1H NMR (300 K, CD2Cl2, 500.13 MHz): δ = 0.98
(t, 6H, CH2CH3, 3J(1H–1H) = 7.2 Hz), 1.32 – 1.44 (m, 4H, CH2CH3),
1.91 – 1.98 (m, 4H, CH2CH2), 2.02 (s, 12H, o-CH3), 2.35 (s, 6H, p-CH3),
4.30 (t, 4H, NCH2, 3J(1H–1H) = 7.3 Hz), 7.08 (s, 4H, m-CH), 7.34 – 7.36 (m,
2H, NCHCHN–nBu), 7.52 – 7.54 (m, 2H, NCHCHN–nBu), 8.18 – 8.20 (m,
2H, NCHN). 11B{1H} NMR (298 K, CD2Cl2, 160.5 MHz) −9.9 (br,
Δν1/2 = 1060 Hz,B(C6F5)3). 13C{1H} NMR (298.1 K, CD2Cl2, 125.7 MHz): δ
= 13.3 (s, CH2CH3), 17.2 (s, o-CH3), 19.7 (s, CH2CH3), 21.1 (s, p-CH3),
32.2 (s, CH2CH2), 51.2 (s, NCH2), 114.4 – 115.0 (m, ipso-CB); 123.1 (s,
NCHCHN–nBu), 124.9 (s, NCHCHN–nBu) 129.2 (s, ipso-Cpara), 130.0 (s,
m-CH), 133.9 (s, ipso-Cortho), 134.3 (s, NCHN), 135.6 – 138.2 (dm, m-CF);
138.9 – 141.4 (dm, p-CF); 142.5 (s, ipso-CN); 146.6 – 149.2 (o-CF); n.o.
(Si(CN)6). 19F{1H} NMR(298 K, CD2Cl2, 470.5 MHz) −135.2 – −134.6 (m;
o-CF), −158.6 – −158.1 (m, p-CF); −165.7 – −165.1 (m, m-CF).
29Si(IG) NMR (300 K, CD3CN, 99.3 MHz) not observed (Si(CN)6).† IR (ATR,
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298 K, 32 scans, cm–1): ν = 406 (w), 445 (w), 470 (m), 488 (w), 501 (w),
̃
556 (w), 575 (s), 587 (m), 616 (m), 631 (m), 686 (s), 729 (w), 742 (m), 771
(m), 797 (m), 843 (w), 863 (m), 874 (w), 973 (vs), 1012 (w), 1069 (w), 1102
(s), 1156 (vw), 1195 (w), 1286 (m), 1385 (m), 1457 (vs), 1519 (s), 1550
(vw), 1562 (vw), 1609 (vw), 1646 (m), 1710 (vw), 1743 (vw), 2271 (vw),
2322 (vw), 2361 (vw), 2374 (vw), 2413 (vw), 2559 (vw), 2576 (vw), 2582
(vw), 2644 (vw), 2749 (vw), 2868 (vw), 2914 (vw), 2938 (vw), 2967 (vw),
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accumulation time: 10 s, 25 scans, 298 K, cm–1): ν = 120 (2), 143 (2), 155
̃
(2), 162 (2), 181 (2), 241 (2), 285 (2), 307 (2), 333 (2), 348 (1), 353 (2),
395 (4), 426 (1), 447 (6), 455 (1), 473 (2), 481 (4), 485 (3), 509 (6), 535
(1), 553 (1), 571 (2), 580 (4), 585 (10), 615 (1), 624 (1), 658 (1), 682 (1),
688 (1), 706 (1), 730 (1), 746 (2), 777 (1), 807 (4), 821 (2), 864 (1), 881
(1), 891 (1), 969 (2), 1025 (1), 1050 (1), 1069 (1), 1104 (1), 1111 (1), 1118
(1), 1125 (1), 1139 (1), 1160 (1), 1235 (1), 1248 (1), 1285 (1), 1314 (1),
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(1), 1458 (1), 1477 (1), 1485 (1), 1521 (1), 1548 (1), 1609 (1), 1647 (2),
2219 (1), 2268 (9), 2347 (1), 2532 (1), 2750 (1), 2867 (1), 2880 (2), 2938
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MeOH (column eluent). †Species were not detected since concentration of
the salt in the solvent is too low.
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Acknowledgements
We thank the Deutsche Forschungsgemeinschaft (DFG SCHU
1170/9-2, STR526/20-2), especially the priority program SPP
1708 for financial support.
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G. M. Sheldrick, Acta Crystallogr. Sect. A Found. Adv. 2015, 71, 3–
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Keywords: cyanides•ion pairs•silicates•structure
elucidation•synthetic methods
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7
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000281
European Journal of Inorganic Chemistry
FULL PAPER
Functionalized Imidazolium Hexacyanidosilicates
Novel hexacyanidosilicate salts of the type [R-Ph(nBu)Im]2[Si(CN)6] (R = 2-Me; 4-Me; 2,4,6-Me = Mes; 2-MeO; 2,4-F and 4-Br;
Im = imidazolium) were synthesized by utilizing a facile salt metathesis process started from K2[Si(CN)6] and the corresponding
substituted imidazolium bromide. Further, the reactivity of the [Si(CN)6]2− dianion towards the Lewis acid B(C6F5)3 was studied, which
led to N–B-bond formation between the [Si(CN)6] core and six boranes, yielding in very bulky {Si[(CN)·B(C6F5)3]6}2− adduct dianion.
8
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