Syntheses, Structures, and Infrared Spectra of the Hexa(cyanido) Complexes of Silicon, Germanium, and Tin

Article abstract of DOI:10.1021/acs.inorgchem.9b00150

The rare octahedral EC₆ coordination skeleton type is unknown for complexes with coordination centers consisting of group 14 elements. Here, the first examples of such EC₆ species, the hexacoordinate homoleptic cyanido complexes E(CN

Full text of DOI:10.1021/acs.inorgchem.9b00150

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Syntheses, Structures, and Infrared Spectra of the Hexa(cyanido)
Complexes of Silicon, Germanium, and Tin
Zoe M. Smallwood, Martin F. Davis, J. Grant Hill, Lara J. R. James, and Peter Portius*
Department of Chemistry, University of Sheffield, Brook Hill S3 7HF, United Kingdom
S
* Supporting Information
ABSTRACT: The rare octahedral EC6 coordination skeleton type is unknown for
complexes with coordination centers consisting of group 14 elements. Here, the first
examples of such EC6 species, the hexacoordinate homoleptic cyanido complexes
E(CN)62−, E = Si, Ge, Sn, have been synthesized from element halides SiCl4, GeCl4
and SnF4 and isolated as salts with PPN counterions (PPN+ = (Ph3P)2N+) on a scale
of 0.2−1 g. Characterization by spectroscopic techniques and by structure
determination through single crystal crystallographic methods show that these
pseudohalogen complexes have effective octahedral symmetry in solution and in the
solid state. Infrared spectra obtained in solution reveal that the T1u symmetric IR-
active vibrations in all three complexes have unusually small oscillator strengths. The
observed reluctance of Si(CN)62−, Ge(CN)62−, and Sn(CN)62− to form from chloro-
precursors was rationalized in terms of Gibbs free energies, which were found by ab
initio calculations at the CCSD(T)-F12b/aug-cc-pVTZ(-PP)-F12 level of theory to be small or even positive. The work
demonstrates that E(CN)62− complexes of silicon, germanium and tin are in fact stable at room temperature and exist as well-
defined units in the presence of noncoordinating counterions. The results add to our understanding of the chemistry of
pseudohalogens and structure and bonding.
coordination. However, the synthesis of P(CN)6− by means of
1. INTRODUCTION
conventional methods from (fluoro)phosphorus precursors is
Negatively charged cyanido, nitrato, cyanato, and azido
hampered by an affinity of P(CN)5 toward F− (590 kJ mol−1)
molecules (Y−) among others, possess reactivity similar to
that is vastly greater than that toward CN− (198 kJ mol−1) and
that of halides. Birckenbach has rationalized this phenomenon
has, thus far, not been realized.14 Intriguingly, tetracyanosilane
by the concept of the pseudohalogen,1,2 which requires
remains unknown despite numerous investigations into
primarily that the Y− species form Y−Y dimers and Y−X
interpseudohalogens upon oxidation, have a stable protonated
pro-ligand form H−Y and produce MYn salts as well as EYn
reactions involving silicon tetrahalides and cyanide
salts.16,21,22 E(CN)6 structures (E = Si−Pb) are interesting
2−
q−
in general as they contain the octahedral EC6 coordination
complexes. As demonstrated by the nonexistence of
skeletons which have hitherto, as opposed to the related
hexaazadiene that was proposed to be formed by the oxidation
3,4
−
covalent ECx networks in silicon carbide containing tetrahedral
SiC4 units,23 not been reported (see ref 23 for related
coordination geometries). Owing to the strength of the Si−C
bonds [ΔHd/(kJ mol−1) = 318.0 to 338.9]24 and the
advantageous match of crystal and coordination geometries,
SiC possesses great hardness and has found many applications
due to this property.23 Recently, germanium and tin complexes
of N3 , not all pseudohalides fulfill the set of criteria
2
q−
completely. Pseudohalogen complexes of the type EYn are
isolable for most p-block elements in groups 13−15: Y = N3
(B−Tl, Si−Sn, P−Bi), NCS (P, Si−Sn), NCO (Si, Ge, Sn),
NO3 (B, Al, Si−Sn). In group 14, they take the form of EL4
and EL62− (E = Si−Pb, L = N3, NO3, NCO, NCS, NCSe).5−12
However, there are only very few homoleptic cyanido
complexes. This group of complexes is restricted to
coordination centers of the less electronegative elements in
+
2+
of the type E(Bu)R2 and Sn(R-2-py)6 containing EC6
coordination skeletons have been prepared with sterically
hindered organic and other ligands. These are, however, either
not octahedral or part of larger coordination networks.25,26
Using strategies involving exchange and transfer reactions
employed previously for the synthesis of azido complexes,6,10,11
ionic and covalent cyanides were investigated as reagents for
−
2−
groups 13 and 15 as P(CN)3, Ga(CN)4 , E(CN)5 (E = In,
Tl, Sb, Bi) and Bi(CN)6
5−16
3−
.
In group 14, the set of known
complexes consist of the E(CN)4 type (E = Ge, Sn), for which,
apart from in situ 119Sn NMR spectral data for the Cl/CN
ligand exchange to form Sn(CN)62−, little analytical data is
available.17−20 CN ligands possess a comparably low oxidation
potential and this effects, for instance, the low thermal stability
of P(CN)5 which readily eliminates cyanogen at ambient
temperature to form P(CN)3.13 The related P(CN)6− complex,
on the other hand, is thought to be stabilized by hyper-
2−
the formation of hexacyanido complexes of the type E(CN)6
(E = Si, Ge, Sn), and the results are reported here.
Received: January 16, 2019
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.9b00150
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
complete dissolution of all solid. To this stirred suspension was added
GeCl4 (0.10 cm3, 0.88 mmol, 1 equiv). The suspension was immersed
into an oil bath and heated to 65 °C for approximately 41 h; after ∼30
min of heating, only a small amount of solid (<100 mg) remained
undissolved. The reaction mixture was allowed to cool to r.t. and
settle and then the colorless supernatant solution was filtered off from
a white filter residue (112 mg) that was discarded. The volume of the
filtrate was the diminished in vacuo until the onset of precipitation
occurred at which stage all solids were redissolved by warming the
vessel in hot air. Crystallization was achieved at −25 °C. An initial
crop of colorless crystals were obtained by filtration. The volume of
the filtrate was further diminished and crystallization induced as
described giving a second crop of colorless crystals which were shown
to be spectroscopically identical to the first. Both crops were
combined to give 2.210 g of mixture of (PPN)2Ge(CN)xCly (x + y =
6), (PPN)Cl, and (PPN)CN. In order to complete the Cl/CN
exchange, a mixture of a part of the combined crop (0.459 g, 0.35
mmol if x = 5), and NaCN (0.186 g, 3.80 mmol, 10.86 equiv), were
suspended in MeCN (15 mL). After ∼5 min stirring at r.t., the
suspension had changed consistency owing to the dissolution of the
germanium complex. The resultant reaction suspension was immersed
in an oil bath set to a temperature of 65 °C. After a total of 196 h
heating, the white suspension was filtered and the filter residue
discarded. The colorless supernatant solution, containing the
hexa(cyanido) complex was concentrated in vacuo until the onset of
precipitation, warmed in hot air to redissolve all solids, and then
placed in a freezer to induce crystallization. This gave colorless
crystals which appear white in bulk under a pale yellow solution,
which were collected by filtration to give pure (PPN)2Ge(CN)6 (2,
0.196 g, 82% with respect to GeCl4) as colorless cuboidal crystals. Mp
188 °C (dec.). Anal. Calcd for C78H60N8P4Ge(1305.92 g mol−1) C,
71.74; H, 4.63; N, 8.58; Cl, 0%. Found C, 71.37; H, 4.66; N, 8.63; Cl,
2. EXPERIMENTAL SECTION
The moisture sensitivity of starting materials for complexes 1−3
(ECl4 or Me3SiCN, see Scheme 1) necessitates the complete
Scheme 1. Reaction Sequences To Form PPN2Si(CN)6 (1),
PPN2Ge(CN)6 (2), and PPN2Sn(CN)6 (3)
a
a
From element halides via [E(CN)xCly]2− intermediates (x + y = 6)
and solvate (Sn(CN)4(MeCN)2, 4a; Sn(CN)4(py)2, py = pyridine,
4b) complexes and (PPN)CN, PPN+ = (PPh3)2N+.
exclusion of air, using standard Schlenk tube and inert gas box
techniques. Extended experimental details are contained in the
Supporting Information, alongside all crystallographic information,
spectra and other analytical details. The raw starting material
bis(triphenylphosphine)iminium cyanide, (PPN)CN, was prepared
from (PPN)Cl and KCN according to Songstad et al.27 However, the
preparation of chlorine-free 1 relies on the complete absence of
chlorine from the PPN starting material which was ensured by the
removal of the KCl byproduct at an intermediate stage and the
application of two batches of KCN in excess each time. Caution!
PPN(CN) and the cyanido complexes 1−4 are toxic. The cyanido
complexes hydrolyze readily; compounds 4a and 4b evolve hydrogen
cyanide gas upon exposure to air.
<0.3%. IR (nujol) ν/cm−1 = 3173, 3145, 3079, 3063, 2251 (br), 2217
̅
(br), 2165, 2159, 1985, 1918, 1906, 1824, 1780, 1684, 1613, 1588,
1575, 1482, 1439, 1436, 1316, 1301, 1284, 1265, 1185, 1162, 1116,
1109, 1073, 1027, 997, 795, 757, 750, 695, 689, 663, 617, 550, 534.
1H NMR (400 MHz, CD3CN, r.t.) δ/ppm = 7.45−7.71 (m, PPN).
13C NMR (100 MHz, CD3CN, r.t., ppm) δ/ppm = 128.2 (d, PPN),
130.3 (m, PPN), 133.2 (m, PPN), 134.6 (s, PPN), 140.0 (s, CN). IR
2.1. Synthesis of (PPN)2Si(CN)6 (1). In a Schlenk tube, a solution
of (PPN)CN (5.012 g, 8.88 mmol, 6.8 equiv) was prepared in the
minimum amount of MeCN. SiCl4 (0.15 cm3, 1.3 mmol, 1 equiv) was
added, and the solution was stirred at 60 °C for 1 h, resulting in the
formation of a small amount of white precipitate. After removal of the
precipitate by filtration, the volume of the colorless filtrate was
diminished in vacuo until the point of saturation was reached and the
solution then cooled to −28 °C for 2 h, forming a white crystalline
solid. The solid was collected by filtration, redissolved in MeCN, and
then transferred into a new solution of (PPN)CN (1.000 g, 1.77
mmol, 1.35 equiv) in the same solvent. The reaction solution was
heated as described above which, again, resulted in the formation of a
small amount of white solid, attributed to some decomposition of a
silicon-containing compound which was removed by filtration. As
before, crystallization was achieved by evaporation of the filtrate in
vacuo until a saturated solution was obtained at room temperature
(r.t.) followed by lowering the temperature to −28 °C. This resulted
in a white crop of large, colorless crystals consisting of pure
PPN2Si(CN)6 (1, 0.696 g, 42%). Mp 230−235 °C (Tdec = 235 °C).
Anal. calcd for C78H60N8P4Si (1261.35 g mol−1): C 74.27, H 4.79, N
(solution, MeCN) ν/cm−1 = 2161, 2135, 2089, 2080(sh), 2051. TOF
̅
MS ES(+) m/z = 538 ([PPN]+, 100). TOF MS ES(−) m/z =
245(100), 141(81), 123(17), spectra dominated by oxo(hydroxo)
germanium species; no signals were attributable to Gex(CN)yz−
.
2.3. Synthesis of Sn(CN)4(MeCN)2 (4a). SnF4 (0.261 g, 1.34
mmol, 1 equiv) was suspended in MeCN (15 mL). Me3SiCN (0.67
mL, 5.36 mmol, 4.0 equiv) was added. After stirring at r.t. for ca. 17 h,
a noticeably thicker white suspension had formed. The suspension
was filtered, resulting in Sn(CN)4(MeCN)2 (0.234 g, 78%) as a
white/cream solid filter residue. Anal. Calcd for C8H6N6Sn(304.78 g
mol−1): C, 31.50; H, 1.98; N, 27.57%. Found C, 5.46; H, 0; N, 5.41.
Sn(CN)4(MeCN)2 as well as Sn(CN)4(py)2 are extremely air
sensitive and produce unreliable data. IR (nujol) ν/cm−1 = 3320
̅
(br), 2321, 2289, 2241 (br), 2182, 1593 (br), 1260, 1207, 1169, 844,
804.
8.88%. Found: C, 74.22; H, 4.58; N, 8.66%. IR (nujol) ν/cm−1
=
2.4. Synthesis of (PPN)2Sn(CN)6 (3) from Sn(CN)4(MeCN)2
(4a). A Schlenk tube was charged with a mixture of 4a (0.209 g, 0.686
mmol, 1 equiv) and (PPN)CN (1.262 g, 2.24 mmol, 3.27 equiv) and
then suspended in MeCN (15 mL). The tube was then immersed in
an oil bath and the suspension stirred and heated to 60 °C for 21 h.
After the reaction mixture had cooled to r.t., a small amount (<10
mg) of solid material was removed by filtration and discarded. The
volume of the pale-yellow filtrate was diminished in vacuo until the
onset of precipitation; any solids visible in the solution were
redissolved by gentle heating and the resultant clear solution cooled
to −28 °C. This resulted in an initial crop of yellow block-shaped
crystals under a yellow supernatant solution, which was collected by
filtration. Further reduction of the volume of the filtrate under
vacuum resulted in a second crop of crystals which were spectroscopi-
cally identical to the first crop. The combined crops gave analytically
pure 3 (0.914 g, 98% with respect to 4a). Mp 271−275 °C. Anal.
̅
3470 (br), 3056, 2696, 2612, 2592, 2584, 2221 (br), 2172, 2163,
2119, 2101, 1985, 1917, 1837, 1687, 1588, 1573, 1481, 1441, 1435,
1325, 1184, 1165, 1161, 1154, 1116, 1073, 1025, 998, 986, 932, 860,
850, 795, 763, 750, 746, 694, 663, 616, 583. 13C NMR (CD3CN) δ/
ppm = 128.2 (d, PPN), 130.3 (m, PPN), 133.2 (m, PPN), 134.5 (s,
PPN), 139.9 (CN). IR (solution, MeCN) ν/cm−1 = 2182, 2175,
2169, 2135. TOF MS ES(−) m/z = 722 ([(PPN)Si(CN)6]−, 100),
158 ([Si(CN)5]−, 47), no signals were observed at 167 ([Si-
(CN)5Cl−]) and 731 ([(PPN)Si(CN)5Cl]− or any other Cl-
containing species in the m/z range 75 to 900). Accurate masses
(a.m.u.) found for [Si(CN)5]−, [(PPN)Si(CN)6]−, 157.9921,
722.1806. Calcd: 157.9928, 722.1813. TOF MS ES(+), m/z = 538
([PPN]+, 100).
2.2. Synthesis of (PPN)2Ge(CN)6 (2). MeCN (20 mL) was added
to (PPN)CN (3.142 g, 5.57 mmol, 6.32 equiv), resulting in almost
B
DOI: 10.1021/acs.inorgchem.9b00150
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Calcd for C78H60N8P4Sn(1351.99 g mol−1) C, 69.30; H, 4.47; N,
8.29; Cl, 0%. Found: C, 68.74; H, 4.54; N, 8.04; Cl, <0.3%. IR (nujol,
analytically pure (PPN)2Sn(CN)6 (3). The degree of progress
of the halide/cyanide exchange reactions to all three E(CN)6
2−
cm−1) ν/cm−1 = 3173, 3146, 3081, 3064, 3039, 3025, 2794, 2787,
̅
complexes was established by C, H, N, and Cl elemental
analyses and electrospray ionization mass spectrometry (see
Figures S23−S25). The mass spectrum of 1 shows fragments
corresponding to [(PPN)Si(CN)6]− at m/z = 722 and of
[Si(CN)5]− at m/z = 158, but none at 731 and 167 that would
correspond to a putative [Si(CN)5Cl]− species. Similarly, the
signals detected of [Sn(CN)5]− and [Sn(CN)3]− in the spectra
of 3 were free of accompanying masses that are likely to occur
if Cl were still present. While the solid hexacyanido complexes
are moderately air-sensitive, the solutions, especially those of 2
and 3, hydrolyze readily. Upon exposure to air, the
decomposition of the solid white powders 4a and 4b also
occurs rapidly and is accompanied by color change and the
release of HCN. Even in hot polar solvent, the latter
compounds are only sparingly soluble thus preventing further
structural analysis.
2696, 2252, 2218 (br), 2157, 2153, 2049 (br), 1985, 1915, 1833,
1616, 1588, 1575, 1482, 1439, 1436, 1260, 1252, 1186, 1179, 1114,
1069, 1028, 1020, 998, 941, 929, 924, 864, 797, 755, 695, 691, 664,
1
616, 550, 532. H NMR (400 MHz, CD3CN, r.t.) δ/ppm = 7.89−
7.22 (m, PPN). 13C NMR (100 MHz, CD3CN, r.t.) δ/ppm = 128.2
(dd, PPN), 130.3 (m, PPN), 133.2 (m, PPN), 134.6(s, PPN), 138.5
(s, CN). IR (solution, MeCN) ν/cm−1 = 2157, 2153(sh), 2135. TOF
̅
MS ES(−), MeCN, m/z = 283 ([((NC)2C3N3)2Na]−, 100), 250
([Sn(CN)5]−, 33), 198 ([Sn(CN)3]−, 20), 194 ([((NC)2C3N3)Na-
(MeCN)]−, 22), 142 ([(C3N3)Na(MeCN)]−, 23). TOF MS ES(+),
MeCN, m/z = 538 ([PPN]+, 100). No signals were observed at 259
([Sn(CN)4Cl−]) and 207 ([Sn(CN)2Cl]−) or any other Cl-
containing species.
3. RESULTS AND DISCUSSION
3.1. Syntheses. At 60−65 °C, solutions containing the
group 14 chloride and the bis(triphenylphosphine)iminium
cyanide (PPN)CN form mixed-ligand complexes of the type
E(CN)xCly2− (x + y = 6) in which the distribution of
chlorido(cyanido)complexes depends on the stoichiometric
ratio of starting material (Scheme 1).
3.2. Crystallographic Studies. Colorless cuboidal single
crystals (1−3) suitable for single-crystal X-ray diffraction were
obtained from hot, saturated MeCN solutions upon cooling to
temperatures below −25 °C. X-ray diffraction studies
performed on specimen of each of these types of crystals
confirmed that in the three investigated reactions, hexa-
(cyanido) complexes had formed as part of 2:1 salts with the
PPN counterions: (PPN)2E(CN)6. This result allows for the
When crystallization is induced in the reaction mixture, the
close chemical similarity of these E(CN)xCly2− complexes
causes the formation of solid solutions. In the case of silicon,
this finding is not only supported by crystallographic data (vide
infra) but also by microanalytically determined CHN content
in these crystals. At CN−/SiCl4 starting material ratios of 2 and
10 mol mol−1, the C, H, and N contents (% w/w) of 69.70,
4.22, and 5.43 and 72.98, 4.41, and 8.12, respectively, were
found to be consistent to within 0.5% with the empirical
2−
structural analysis of the E(CN)6 complexes of Si (1), Ge
(2), and Sn (3) given below (see also the Supporting
Information, p S9 ff). The EC6 coordination skeletons of the
investigated complexes adhere closely to the octahedral
symmetry (Figures 1−3) with only small deviations in the
2−
formulas Si(CN)2.9Cl3.1 and Si(CN)5.2Cl0.82−. This suggests
that complete Cl/CN exchange requires molar ratios above 50
mol mol−1, rendering this direct one-step method expensive.
Since the (PPN)2Si(CN)xCly salts are separable from the
reaction mixture by crystallization, decoordinated Cl− can be
removed as (PPN)Cl and a supposed reaction equilibrium
2−
shifted toward Si(CN)6 by exposing (PPN)2Si(CN)xCly to
further amounts of (PPN)CN in a second step under
otherwise identical conditions. After this treatment, the Cl
content in the newly crystallized material had decreased to
below 0.3% which translates to coefficients of x > 5.9 and y <
0.1. GeCl4 and SnCl4 also react with (PPN)CN to form
chlorido(cyanido) complexes. However, in these cases the
preparation of the Cl-free complexes is unfeasible due to an
even less favorable position of the equilibrium. Instead, the
intermediary (PPN)2Ge(CN)xCly was converted in the second
step to (PPN)2Ge(CN)6 (2) by applying a large excess of
NaCN instead of (PPN)CN and a longer reaction time (196
h). It was found that AgCN is not suitable as a CN-ligand
transfer reagent since the crystallization from the solution
containing (PPN)2Ge(CN)xCly and AgCN removes the PPN
cation as part of the silver salt (PPN)Ag(CN)2,28 which was
identified by single crystal XRD (see the Supporting
Information, p 29). This reaction is also likely to occur if
AgCN is used in syntheses of the Si and Sn analogs 1 and 3.
SnCl4 showed insufficient reactivity in the presence of either
NaCN or (PPN)CN, hence, Sn(CN)62− cannot be obtained by
direct ligand exchange using ionic reagents. It was found that
SnF4 reacts readily with Me3Si-CN in pyridine or acetonitrile
under formation of the adducts Sn(CN)4(L)2 (L = MeCN, 4a;
pyridine, 4b), which react further with (PPN)CN to afford
2−
Figure 1. Thermal ellipsoid plots of the Si(CN)6 complexes of 1
drawn at the 50% probability level; black, C; blue, N; gray, Si, “i”
denotes symmetry-equivalent sites. Bond lengths [Å] and selected
angles [°]: Si(1)−C(1) 1.9501(15), Si(1)−C(2) 1.9547(15), Si(1)−
C(3) 1.9588(15), C(1)−N(1) 1.152(2), C(2)−N(2) 1.125(2),
C(3)−N(3) 1.115(2); C(1)−Si(1)−C(2) 89.55(6), C(1)−Si(1)−
C(2) 90.45(6), C(1)−Si(1)−C(3) 88.61(6), C(1)−Si(1)−C(3)
91.39(6), C(2)−Si(1)−C(3) 89.08(6), C(2)−Si(1)−C(3)
90.92(6), Si(1)−C(1)−N(1) 178.01(13), Si(1)−C(2)−N(2)
177.59(14), Si(1)−C(3)−N(3) 175.27(14).
C
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2−
Figure 3. Thermal ellipsoid plots of the Sn(CN)6 complex of 3
drawn at the 50% probability level; black, C; blue, N; gray, , Sn, “i”
denotes symmetry-equivalent sites. Bond lengths [Å] and selected
angles: Sn(1)−C(3) 2.203(2), Sn(1)−C(1) 2.225(2), Sn(1)−C(2)
2.229(2), N(1)−C(1) 1.134(3), N(2)−C(2) 1.146(3), N(3)−C(3)
1.159(3); C(3)−Sn(1)−C(1) 91.65(8), C(3)−Sn(1)−C(1)
88.35(8), C(3)−Sn(1)−C(2) 88.43(8), C(3)−Sn(1)−C(2)
88.92(8), C(1)−Sn(1)−C(2) 91.08(8), C(3)−Sn(1)−C(2)
91.58(8), C(1)−Sn(1)−C(2) 88.92(8), N(1)−C(1)−Sn(1)
174.89(19), N(2)−C(2)−Sn(1) 175.73(19), N(3)−C(3)−Sn(1)
179.1(2).
2−
Figure 2. Thermal ellipsoid plots of the Ge(CN)6 complex of 2
drawn at the 50% probability level; black, C; blue, N; gray, Ge. Bond
lengths [Å] and selected angles [°]: Ge(1)−C(1) 2.0584(15),
Ge(1)−C(2) 2.0441(15), Ge(1)−C(3) 2.0491(17), Ge(1)−C(4)
2.0480(15), Ge(1)−C(5) 2.0573(15), Ge(1)−C(6) 2.0407(16),
C(1)−N(1) 1.1455(19), C(2)−N(2) 1.145(2), C(3)−N(3)
1.146(2), C(4)−N(4) 1.145(2), C(5)−N(5) 1.146(2), C(6)−N(6)
1.144(2); C(1)−Ge(1)−C(6) 90.99(6), C(2)−Ge(1)−C(5)
179.54(6), C(6)−Ge(1)−C(5) 91.5251(6), C(2)−Ge(1)−C(4)
89.97(6), C(6)−Ge(1)−C(4) 88.52(6), C(5)−Ge(1)−C(4)
89.8685(6), C(2)−Ge(1)−C(3) 91.85(6), C(6)−Ge(1)−C(3)
177.68(6), C(5)−Ge(1)−C(3) 88.58(6), C(4)−Ge(1)−C(3)
93.80(6), C(2)−Ge(1)−C(1) 89.92(6), C(6)−Ge(1)−C(1)
90.99(6), C(5)−Ge(1)−C(1) 90.25(6), C(4)−Ge(1)−C(1)
179.50(5), C(3)−Ge(1)−C(1) 86.70(6), N(1)−C(1)−Ge(1)
176.56(14), N(2)−C(2)−Ge(1) 174.12(14), N(3)−C(3)−Ge(1)
174.90(13), N(4)−C(4)−Ge(1) 174.92(13), N(5)−C(5)−Ge(1)
177.24(13), N(6)−C(6)−Ge(1) 176.14(13).
Cl, and by implication similarly sized ligands), can be ruled out
as sufficiently abundant contaminant. Support for this
conclusion is found in the Cl contents of the substances
used to grow the crystals for X-ray data collection, which were
below the microanalytical detection limit (0.3%). This implies
that the x/y ratio, which accounts for any Cl ligands potentially
present in the crystals, is close to or above 5.9/0.1. Therefore,
no more than one additional electron per formula unit is
unaccounted for by a structure model that assumes x/y = 6/0
(further discussion of residual electron densities relating to Cl
can be found in the Supporting Information). The system
(PPN)2Si(CN)xCly (x + y = 6) is particularly prone to the
formation of mixed crystals from solutions of incompletely Cl/
CN-exchanged complexes, which results in residual electron
density at distances from the coordination center typical for
Si−Cl bonds in other hexacoordinate Si(IV) complexes (2.25−
2.32 Å), but also in a reduction in the unit cell volume in line
with typical crystallographic volumes of ligands (y ∼ 2.3, V =
6490.5(4) Å3, y < 0.1, V = 6662.7(2) Å3, for details see the
Supporting Information, p S9).
interligand angles of no more than 3.80(6) and 2.32(6)° from
the ideal geometry of 90 and 180°, respectively, which is
ascribed to the differences in the packing imposed by the
crystal systems (1, orthorhombic; 2 and 3, monoclinic, Figure
4). The cyanido ligands adopt the essentially linear end-on-C
coordination (κ(C)) mode that has been observed previously
for other p-block complexes with coordination centers of
groups 13 and 15.15,29 Structure models tested during
crystallographic structure refinement that feature isocyanido
ligands E(CN)x(NC)y2− all were significantly inferior in
predicting the diffraction data, leading to substantially
increased disagreement factors (R).
2−
Within each E(CN)6 complex, the lengths of C−N and
E−C bonds vary only slightly at a level similar to that observed
previously in crystals of K3Fe(CN)6,27 for instance (see Table
1). This variation is attributable to the crystal lattice-imposed,
noncubic packing around the complex anions resulting in
various sets of cation−complex anion contacts (Figure 4),
rather than to electronic structure effects arising from the
complexes themselves. It is a well-known fact that impurities in
crystals may lead to deficiencies in crystal structure models
(vide supra, discussion on intermediary chlorido(cyanide)
species). Chlorine as the most likely candidate for forming
solid solutions of the type (PPN)2E(CN)xXy (x + y = 6, X =
A comparison with the formula unit volumes found in the
crystal structures of the related PPN2E(N3)6 salts (all P1
̅
symmetry)6,10,11 reveals a trend, in which the E(CN)62−
2−
complexes occupy consistently less space than E(N3)6
complexes: ΔV/Å3 = −28 (Si), −66 (Ge), −50 (Sn).
3.3. Spectral Properties. Group theory requires isotopi-
q−
cally pure octahedral E(CN)6 complexes to exhibit only a
single band in the region of the CN stretches (νCN) of the
IR spectrum due to the t1u symmetric fundamental stretching
vibrations. In MeCN solution, the hexacyanido complexes
show this band at 2169 cm−1 (1), 2161 cm−1 (2), and 2157
D
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Figure 5. Transmission IR spectra of (PPN)CN (−), PPN2Si(CN)6
○
○
○
(1 ), PPN2Ge(CN)6 (2 ), and PPN2Sn(CN)6 (3 ) between
2185 and 2135 cm−1 (top, mulls) and of MeCN solutions of
(PPN)CN (4.0 × 10−2), 1 (2.0 × 10−2), 2 (1.0 × 10−2), and 3 (9.9 ×
10−3) between 2180 and 2145 cm−1 (bottom, concentrations/mol
dm−3 given in parentheses). The integrated intensities of those bands
at 1186 cm−1 and 739−782 cm−1 attributed to the PPN cation were
used for normalization.
Figure 4. Projection of the unit cells of 1 (top) and 3 (bottom) down
the crystallographic a axes; C, dark gray; N, blue; P, orange; Si,
yellow; Sn, olive; H, light gray; ellipsoids set at the 50% level.
the CN ligand and the ineffective back-donation into the π*
acceptor levels due to the lack of d-electrons at the
coordination center. Compared to the related transition
cm−1 (3), respectively (see Figure 5 bottom and Table 2).
Compared to their azido analogues (see the references given
above), the molar extinction coefficients of these bands are
very small but still considerably larger than that of the CN−
anion itself at 2052 cm−1 in the same medium (see Figures
S1−S13). The shift to higher wavenumbers in comparison to
the latter is caused by electron donation from the σ* orbital of
33
3−
3−
metal complexes Fe(CN)64−, Ti(CN)6
and Fe(CN)6 ,
which display CN stretches at 2098, 2071, and 2135 cm−1,
respectively, those of the title complexes are, intriguingly, all at
much higher frequencies and closer to those of the covalently
bound tetracoordinate Me3E−CN cyanides at 2190 cm−1 (E =
Table 1. Key Structural Parameters of the E(CN)62− Complexes of 1−3 in Comparison with K3M(CN)6 (M = Cr, Fe) Derived
from X-ray Diffraction Studies
a
a
compound
dC−N/Å
d
E−C/Å
∠E−C−N Δmax/°
∠C−E−C Δmax/°
∠C−E−C Δmax/°
ref
b
E = Si (1)
1.115(2)−1.152(2)
1.144(2)−1.146(2)
1.134(3)−1.159(3)
1.131(22)−1.167(26)
1.099(22)−1.167(17)
1.950(2)−1.959(2)
2.041(2)−2.059(2)
2.203(2)−2.229(2)
1.927(14)−1.971(29)
2.057(12)−2.100(10)
4.7(1)
5.9(1)
5.1(1)
8.6(1.5)
2.7(1.0)
1.39(6)
3.80(6)
1.65(8)
1.6(7)
0
d
d
d
c
E = Ge (2)
2.32(6)
0
0
c
E = Sn (3)
K3Fe(CN)6
K3Cr(CN)6
30, 31
32
1.1(5)
1.0(5)
a
b
c
d
Minimum−maximum values given. Data for 130 K. Data for 100 K. This work.
E
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corroborate the findings in solution, 13C−119Sn cross-polar-
ization experiments were performed at 30 s delay time.
However, under these parameters, only signals that belong to
the PPN cation were observed, similar to those detected earlier
by direct observation of 13C. Only minor differences between
(PPN)Cl and the complexes are noticeable and signals of CN
Table 2. Frequencies of the νCN Band Absorption Maxima
Observed in the Transmission IR Spectra of Compounds 1−
4 and (PPN)CN and Chlorido(cyanido) Complexes
a b
,
a c
,
compound
(PPN)CN
(PPN)2Si(CN)6 (1)
(PPN)2Ge(CN)6 (2)
(PPN)2Ge(CN)xCly
(PPN)2Sn(CN)6 (3)
(PPN)2Sn(CN)xCly
solid
solution
2074, 2058, 2047
2172, 2163 (0.89)
2164, 2159 (0.70)
2155, 2053
2157, 2153, 2146 (1)
2157, 2153
e
d
d
d
d
1
2168.8 (0.53, 4.74(6))
2160.8 (0.33, 5.64(6))
ligand(s) could not be attributed due to overlap of bands. H
T1 measurements on (PPN)2Sn(CN)6 showed long relaxivity
times of ∼25 s. Therefore, it can be extrapolated that 15N and
13C will require extremely long acquisition times in the order of
weeks and these were deemed unfeasible. A 15N MAS NMR
spectrum for compound 3, obtained at a relaxation time of
∼125 s, displayed only one very weak signal at ∼362 ppm,
which is assigned to the PPN cation.
d
d
2157.3 (1, 5.68(9))
Sn(CN)4(MeCN)2 (4a) 2182
f
f
Sn(CN)4(py)2 (4b)
2165
2−
Pb(CN)6
a
b
c
Frequency at band maximum/cm−1. Nujol mulls. In MeCN.
Relative νCN band area,
While all attempts to observe the 29Si and 73Ge resonance of
(PPN)2Si(CN)6 and (PPN)2Ge(CN)6 failed due to the lack of
sensitivity of the spectrometer probe, the 119Sn MAS NMR
spectrum of PPN2Sn(CN)6 displays a peak in the range of
−600 to −1000 ppm, at δ(119Sn) = −871 ppm, which
corresponds to the peak at ca. − 879 ppm of the same
compound in MeCN solution (1J(119Sn, 13C) = 1218 Hz). The
variance of δ(119Sn) with that published previously at −916.2
ppm20 is large. The latter is the result of an assignment for in
d
0.02, and fwhm/cm−1 in parentheses,
e f
areas based on compound 3 set to unity. Not observed. Insufficiently
soluble.
Si, + 21 cm−1),34 2181 cm−1 (E = Ge, + 20 cm−1),35 and 2175
cm−1 (E = Sn, + 18 cm−1).36,37 This finding suggests that the
E−C bonds are unusually strong and covalent despite the
2−
hypercoordinate character of the E(CN)6 complexes. This
2−
situ generated Sn(CN)6 in CH2Cl2 solution; the authors
conclusion is also reflected in the IR spectra of the complexes
in the microcrystalline form where, however, additional νCN
bands are present (Figure 5 top). Again, the analytically
confirmed purity of each sample (vide supra) rules out any
assignment to chlorido(cyanido) species as components of a
solid solution. The additional bands are more likely to be
caused by the crystal packing-imposed symmetry at the sites of
the E(CN)6 complexes, which transforms with either the D2h
point group (1 and 3) or C1 (2). Under D2h, three fundamental
νCN stretches of E(CN)6 are IR-active (B1u, B2u, and B3u). As
these complexes have essentially octahedral geometry, their
symmetry is closely related to D3d and two of the three IR-
active νCN stretches (A2u and Eu) become degenerate so that
only two absorption bands result, which aligns with the
observations made in the spectra in the mull of 1 (D3h, 2172
cm−1 intense, 2163 cm−1 medium) and 2 (D3h, 2164 cm−1
medium, 2159 cm−1 intense), whereas the greater distortion of
3 produces three bands (D2d, 2157 cm−1 intense, 2153 cm−1
intense, 2146 cm−1 weak shoulder).
2−
state that Sn(CN)6 could not be isolated. Given the
independent, multiply verified identity and purity of the
substance obtained as compound 3, and the similarity between
MAS and solution 119Sn NMR spectra of this substance, we
suggest that the previously observed chemical shift belongs to a
2−
Sn-containing species other than Sn(CN)6 (see also Figures
S14−S22).
3.4. Theoretical Studies. In order to rationalize the
experimental findings, gas phase and solution energies of CN−,
Cl−, E(CN)4, E(CN)5−, E(CN)62−, and E(CN)5Cl2− were
calculated using density functional theory and coupled cluster
methods (see the Supporting Information for full computa-
tional details). These energies are related to each other
according to the reactions analogous to those evaluated by
Haiges et al.15 (reactions 1−3) shown below. In view of earlier
reports on trimethylsilylcyanide, which exists as an equilibrium
mixture with the N-bonded silylisocyanide through a rapid CN
group exchange reaction,34 the relative stability of the linkage
isomers E(CN)5(NC)2− was assessed relative to the homo-
leptic cyanido complexes, E(CN)62− (E = Si−Sn) (reaction 4).
The frequency of the νCN stretch decreases from 1 to 3, a
trend which matches that found in other pseudohalogen
2−
complexes such as E(N3)6 and in the series of Me3E−CN
E(CN)4 + CN− → E(CN)5−
E(CN)5− + CN− → E(CN)62−
(1)
(2)
compounds (E = Si, Ge, Sn, for refs see above). Due to their
insolubility in inert solvents suitable for IR spectral
investigation in the region of interest, spectra of 4a and 4b
solutions were unattainable.
E(CN)5Cl2− + CN− → E(CN)62− + Cl− (3)
E(CN)62− → E(CN)5(NC)2− (4)
13C MAS NMR spectra were recorded of microcrystalline
samples for all three hexacyanido complexes. The peaks arising
from CN ligands could not be resolved due to overlap with the
intense peaks of the PPN cations. 13C NMR spectroscopic
studies of solutions of compound 1, however, display a well-
resolved CN group resonance (δ(13C) = 139.9 ppm) with a
chemical shift in between those of cyanosilanes, e.g., Me3Si-CN
(126.9 ppm),38 and cyanide salts, e.g., (PPN)CN (166.5 ppm
in the same solvent). Similar claims can be made for 2 and 3
(Me3Ge−CN, 127.0 ppm;39 Me3Sn−CN, ∼134 ppm).40 13C
NMR spectra of dmso-d6, solutions of charge-neutral 4b, show
a single resonance attributable to the CN ligands at δ = 113.8
ppm, alongside the three signals of symmetrically coordinated
pyridine ligands at 149.6, 136.1, and 123.9 ppm. To
Geometry optimizations and harmonic frequency calculations
were carried out at the PBE0 level of theory41 using the aug-cc-
pV(T+d)Z basis set for C, N, Si, and Cl,42 where the “+d”
denotes additional tight d functions for second row atoms, and
the aug-cc-pVTZ-PP basis for the heavier atoms.43 The latter is
matched to small-core relativistic pseudopotentials replacing
10, 28, and 60 electrons for Ge, Sn and Pb, respectively. The
−
complexes E(CN)4, E(CN)5 , E(CN)5Cl2− and E(CN)62−, E
= Si−Pb, were optimized and were found to have Td, D3h, C4v
and Oh symmetry, respectively. Frequency calculations of the
F
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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 3. Observed (obs) and Calculated (calc) Bond Lengths (d/Å) and Frequencies (ν/cm−1) and Intensities of the CN
Stretching Vibrations of the E(CN)6 (a) and E(CN)5(NC)2− (b) Complexes
2−
a
a
b
c
E−Lobs
E−Lcalc
C−Nobs
C−Ncalc
νCN(obs)
νCN(calc)
(a)
(b)
(a)
(b)
(a)
(b)
(a)
1.956(10)
2.052(7)
2.222(14)
1.961
1.144(16)
1.152(2)
1.156(14)
1.156
1.156
1.166
1.156
1.156
1.166
1.157
1.156
2168.8 (0.53)
2160.8 (0.33)
2157.3 (1)
2281.8(0.08)
2284.4(0.34)
2202.6(207)
2277.2(0.02)
2281.6(0.00)
d
d
g
g
g
E = Si
1.957
1.863
e
e
h
2.059
d
d
E = Ge
2.048
e
e
h
1.999
2194.0(195)
2276.0(1.57)
2279.5(1.11)
2.238
d
d
E = Sn
E = Pb
2.227
e
e
h
2.168
1.167
1.157
2191.5(193)
2265.3(2.43)
2.329
a
Thermal motion in the crystal may produce an apparent shrinkage of molecular dimensions and is considered by calculating instantaneous bond
lengths Di, which are estimated by Di ≈ D0 + |UA − UB|/D0 using the distances D0 and thermal displacement parameters UA, UB for atoms A, B of
the refined crystallographic structure solution; E−Cobs and C−Nobs are listed as unweighted mean xu of Di with either standard deviation σ = [Σ(Di
b
− xu)2/(n − 1)]0.5 or distribution of means σm = σi/n0.5, whichever is larger, in parentheses; n = 3, Si, Sn; n = 6, Ge. In MeCN solutions, relative
c
d
e
g
band areas in parentheses. Oscillator strength (in km mol−1) given in parentheses. Cyanido ligands. Isocyanido ligand. E-symmetric C−N
h
stretches. Isocyanido C−N stretch.
Table 4. Reaction Energies (in kJ mol−1) at 298 K for the
Formation of the E(CN)6 Complexes
minimum geometries obtained after optimization resulted in
no imaginary frequencies (see the Supporting Information p
2−
S68). Bond lengths and angles derived from the calculated
geometries for the E(CN)6 complexes 1−3 and those
a
b
c
e
E
reaction
ECCSD(T)
ΔGtherm
ΔGsolv
ΔGsol
2−
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
−295.4
+26.5
−50.8
+48.4
+57.9
+18.2
+147.6
−176.9
+20.6
−99.3
−92.4
−12.0
+4.4
−44.1
−44.9
−2.8
+12.5
−74.2
−57.6
+7.9
+10.2
−32.5
−13.1
+12.7
observed crystallographically (Table 3) are within, or close to,
the experimental 1σ uncertainty. Therefore, it is suggested that
the PBE0/aug-cc-pV(T+d)Z(-PP) model is sufficiently reliable
for predicting geometries and spectral properties, and can be
used in conjunction with coupled cluster methods for
energetics.
Si
−253.3
+60.2
−39.5
+45.5
+54.7
+17.6
+163.7
−159.9
+19.1
Ge
Remarkably, the CN bond lengths are influenced only
slightly by a change of the coordination center, which indicates
that the electronic situation of the CN bond is only
marginally dependent on the central atom in group 14. The
calculated vibrational frequencies and absorption cross sections
validate the IR spectroscopic findings reported above
suggesting that the transition dipole moments44 of the IR-
active T1u-symmetric CN stretches have a minimum for
−302.5
+20.6
−27.2
+42.8
+54.8
+17.0
+185.4
−133.0
+18.1
Sn
Pb
−271.4
+48.9
−19.1
+40.3
+52.1
+16.5
+198.6
−114.1
+15.3
2−
Ge(CN)6 and a maximum for Pb(CN)62−. The calculated
a
Gas-phase data at the CCSD(T)-F12b/aug-cc-pVTZ(-PP)-F12 level
of theory using PBE0-optimized geometries. thermodynamic Gibbs
free energy (298 K) at the PBE0 level. Gibbs free energy of solvation
in acetonitrile at the PBE0 level using the SMD approach. solution-
b
frequencies for the isocyanido CN stretches in the hypothetical
complexes of the type E(CN)5(NC)2− (Si−Sn) are predicted
to be about 80 cm−1 below those observed, and their
absorption coefficients to be 3−4 orders of magnitude more
intense than those of the cyanido ligands. In the recorded
spectra, this region is free of such bands; therefore, we suggest
that if isocyanido complexes are present in solution, then at a
very low concentration.
Table 4 displays the net electronic energy changes for the
reactions 1−3, as well as the correction terms for changes in
the Gibbs free energies caused by thermal and solvent effects.
As can be expected, the Lewis acid−base reactions of the
attachment of a cyanido anion to the tetracoordinate
tetracyano complex are highly exothermic, whereas the
attachment of another cyanido ligand to form the hexacoordi-
nate complexes is endothermic. While both types of reactions
are endergonic at 298 K, solvent effects cause a large reduction
in the Gibbs free energies so that according to the model used
reactions 1 and 2 are spontaneous at r.t. for all evaluated
coordination centers.
c
e
phase reaction energies.
complexes in the by Cl/CN exchange reactions. The solvent-
effect-corrected Gibbs free energies for 298 K, the temperature
at which 1−3 were isolated from the reaction solutions, clearly
corroborate the experimentally observed trend in the reduction
of the driving force for this reaction. On the basis of free Gibbs
energies, ΔGsol, for solvated complexes, concentration ratios of
E(CN)62−/E(CN)5Cl2− at 298 K can be calculated as 1.3 ×
102, 3.1, 4.1 × 10−2, and 6.0 × 10−3, respectively, which show
2−
that within this model reaction 3 to form Sn(CN)6 from
SnCl4 with soluble ionic cyanides cannot be driven to
completion. The ΔGsol energies furthermore indicate a clear
2−
preference for homoleptic hexacyanido complexes E(CN)6
over their E(CN)5(NC)2− linkage isomers.
CONCLUSION
■
Hexa(cyanido) complexes of the type E(CN)62−, E = Si, Ge,
Sn, have been synthesized, isolated, and fully characterized as
saltlike compounds with PPN counterions. The PPN2E(CN)6
Since the synthesis of complexes 1−3 was investigated with
ECl4 as starting material (vide supra), it is the E(CN)5Cl2−
complexes that are the ultimate intermediates to the hexacyano
G
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compounds are moderately air sensitive and dissolve readily in
polar aprotic solvents without noticeable dissociation or
linkage isomerization of the E(CN)6 complex anions. The
REFERENCES
■
̈
(1) Birckenbach, L.; Kellermann, K. Uber Pseudohalogene (I). Ber.
Dtsch. Chem. Ges. B 1925, 58, 786−794.
(2) Golub, A. M.; Kohler, H.; Skopenko, V. V. Chemistry of
2−
synthetic methodologies applied to these hypercoordinate
complexes are partially based on those used previously for the
N3, NCS and NCO analogues.6,8,45 However, more forcing
conditions are required for the final reaction step E(CN)5Cl2−
̈
Pseudohalides; Elsevier,: New York, 1986.
(3) Greschner, M. J.; Zhang, M.; Majumdar, A.; Liu, H.; Peng, F.;
Tse, J. S.; Yao, Y. A New Allotrope of Nitrogen as High-Energy
Density Material. J. Phys. Chem. A 2016, 120, 2920−2925.
(4) Najafpour, J.; Foroutan-Nejad, C.; Shafiee, G. H.; Peykani, M. K.
How does electron delocalization affect the electronic energy? A
survey of neutral poly-nitrogen clusters. Comput. Theor. Chem. 2011,
974, 86−91.
2−
+ CN− → E(CN)6 + Cl−, the reasons for which were
identified with the help of systematic DFT and coupled cluster
calculations. According to these calculations it is primarily the
reduction in the net-loss of electronic energy in the reaction
involving tin and, presumably, the similarity in Sn−CN and
Sn−Cl bond strengths which cause the supposed reaction
equilibrium to lie on the side of the starting material.
Crystallographic studies have demonstrated that the CN
ligands prefer the κ(C)-cyanido form in an only marginally
distorted octahedral ligand sphere which demonstrates the
viability of homoleptic octahedral complexes with the unusual
EC6 coordination skeletons in group 14.
(5) Wiberg, E.; Michaud, H. Silicon tetraazide, Si(N3)4. Z.
Naturforsch., B: J. Chem. Sci. 1954, 9, 500.
(6) Filippou, A. C.; Portius, P.; Schnakenburg, G. The
Hexaazidosilicate(IV) Ion: Synthesis, Properties and Molecular
Structure. J. Am. Chem. Soc. 2002, 124, 12396−12397.
(7) Seiler, O.; Burschka, C.; Goetz, K.; Kaupp, M.; Metz, S.; Tacke,
R. The new λ6-Si-silicate dianion [Si(NCO)6]2− synthesis and
structural characterization of [K(18-crown-6)]2[Si(NCO)6]. Z.
Anorg. Allg. Chem. 2007, 633, 2667−2670.
(8) Heininger, W.; Stucka, R.; Nagorsen, G. A new silicate anion:
[Si(NCS)6]2−. Z. Naturforsch., B: J. Chem. Sci. 1986, 41, 702−707.
(9) Heininger, W.; Polborn, K.; Nagorsen, G. A further silicate
anion: [Si(NCSe)6]2−. Z. Naturforsch., B: J. Chem. Sci. 1988, 43, 857−
861.
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b00150.
(10) Filippou, A. C.; Portius, P.; Neumann, D. U.; Wehrstedt, K.-D.
The Hexaazidogermanate(IV) Ion: Syntheses, Structures, and
Reactions. Angew. Chem., Int. Ed. 2000, 39, 4333−4336.
(11) Campbell, R.; Davis, M. F.; Fazakerley, M.; Portius, P. Taming
Tin(IV) Polyazides. Chem. - Eur. J. 2015, 21, 18690−18698.
(12) Portius, P.; Peerless, B.; Davis, M.; Campbell, R. Homoleptic
Poly(nitrato) Complexes of Group 14 Stable at Ambient Conditions.
Inorg. Chem. 2016, 55, 8976−8984.
Details of the crystallographic structure determination
for compounds 1−3 and ((PPN)Ag(CN)2, FTIR, NMR
and mass spectra, Cartesian coordinates of the computa-
tional models and further preparative and experimental
details (PDF)
̈
(13) Gall, H.; Schuppen, J. Uber die Valenz-Grenze bei
̈
Phosphorcyaniden und Phosphorrhodaniden. Ber. Dtsch. Chem. Ges.
B 1930, 63, 482−487.
Accession Codes
CCDC 1820145, 1820360, 1820362, and 1856451 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing 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.
̈
(14) Blasing, K.; Ellinger, S.; Harloff, J.; Schulz, A.; Sievert, K.;
̈
̈
Taschler, C.; Villinger, A.; Zur Taschler, C. Lewis Acid Catalyzed
Synthesis of Cyanidophosphates. Chem. - Eur. J. 2016, 22, 4175−
4188.
(15) Haiges, R.; Deokar, P.; Vasiliu, M.; Stein, T. H.; Dixon, D. A.;
Christe, K. O. Preparation and Characterization of Group 13
Cyanides. Chem. - Eur. J. 2017, 23, 9054−9066.
(16) Arlt, S.; Harloff, J.; Schulz, A.; Stoffers, A.; Villinger, A. Cyanido
Antimonate(III) and Bismuthate(III) Anions. Inorg. Chem. 2016, 55,
12321−12328.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: p.portius@shefield.ac.uk.
ORCID
J. Grant Hill: 0000-0002-6457-5837
Peter Portius: 0000-0001-8133-8860
Present Address
(17) Menzer, W. Zur Kenntnis des Germaniumtetracyanids. Angew.
Chem. 1958, 70, 656.
̌
̈
(18) Jung, S.; Renz, F.; Klein, M.; Menzel, M.; Boca, R.; Stoßer, R.
Molecular switching in iron complexes bridged via tin-cyanides
̈
observed by Mossbauer and ESR spectroscopy. J. Phys. Conf. Ser.
2010, 217, 012027.
(19) Bither, T. A.; Knoth, W. H.; Lindsey, R. V.; Sharkey, W. H.
Trialkyl- and Triaryl(iso)cyanosilanes. J. Am. Chem. Soc. 1958, 80,
4151−4153.
(20) Dillon, K. B.; Marshall, A. Tin-119 Nuclear Magnetic
Resonance Studies of some Pseudohalogenoderivatives of [SnX6]2−
(X = CI or Br). J. Chem. Soc., Dalton Trans. 1987, 315−317.
(21) Emerson, K. The preparation and structure of group V
tricyanides. Ph.D. Thesis. University of Minnesota, Minneapolis, MN,
1960.
(22) Howdeshell, J. P. The reactions of tris (trimethylsilyl) phospine
and attempted synthesis of silicon tetracyanide. Ph.D. Thesis.
University of Wyoming, Laramie, WY, 1973.
(23) Fan, J.; Chu, P. K.-H. Fabrication, Structure, Properties. In
Silicon Carbide Nanostructures. Engineering Materials and Processes;
Springer International Publishing: Switzerland, 2014.
M.F.D.: Nanoco Technologies Ltd., Manchester M13 9NT,
United Kingdom.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the University of Sheffield; in
particular, the authors thank the university for the award of a
graduate teaching assistantship to ZS. The authors thank Prof.
Wolfgang A. Herrmann (TU Munchen) for his suggestions,
̈
Dr. Sandra van Meurs for recording NMR spectra and Harry
Adams and Craig Robertson for their technical assistance in
obtaining crystallographic data.
H
DOI: 10.1021/acs.inorgchem.9b00150
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(24) Steele, W. C.; Nichols, L. D.; Stone, F. G. A. The
Determination of Silicon-Carbon and Silicon-Hydrogen Bond
Dissociation Energies by Electron Impact. J. Am. Chem. Soc. 1962,
84, 4441−4445.
(45) Portius, P.; Davis, M. A new hexakis(isocyanato)silicate(IV)
and the first neutral Lewis-base adducts of silicon tetraisocyanate.
Dalton Trans. 2010, 39, 527−532.
NOTE ADDED IN PROOF
Since this work was submitted, a paper dealing with the
synthesis and structure of Si(CN)6 appeared online: Schulz,
(25) Schrader, I.; Zeckert, K.; Zahn, S. Dilithium
Hexaorganostannate(IV) Compounds. Angew. Chem., Int. Ed. 2014,
53, 13698−13700.
■
2−
(26) Yang, Y.; Panisch, R.; Bolte, M.; Muller, T. Bis-alkene
̈
A.: Harloff, J.; Michalik, D.; Nier, S.; Stoer, P.; Villinger, A.
Cyanidosilicates − Synthesis and Structure. Angew. Chem. Int.
Ed., https://doi.org/10.1002/anie.201901173.
Complexes of Stannylium and Germylium Ions. Organometallics
2008, 27, 4847−4853.
(27) Martinsen, A.; Songstad, J. Preparation and properties of some
bis(triphenylphosphine)iminium salts, [(Ph3P)2N]X. Acta Chem.
Scand. 1977, 31a, 645−650.
(28) Jaafar, M.; Liu, X.; Dielmann, F.; Hahn, F. E.; Al-Farhan, K.;
Alsalme, A.; Reedijk, J. Synthesis, structure and spectroscopic
properties of bis(triphenylphosphane)iminium(chlorido) (cyanido)
argentates(I). Inorg. Chim. Acta 2016, 443, 45−50.
(29) Deokar, P.; Leitz, D.; Stein, T. H.; Vasiliu, M.; Dixon, D. A.;
Christe, K. O.; Haiges, R. Preparation and Characterization of
Antimony and Arsenic Tricyanide and Their 2,2′-Bipyridine Adducts.
Chem. - Eur. J. 2016, 22, 13251−13257.
(30) Vannerberg, N.-G. The OD Structures of K3Fe(CN)6 and
K3Co(CN)6. Acta Chem. Scand. 1972, 26, 2863−2876.
(31) Shimanouchi, T.; Nakagawa, I. Infrared spectroscopic study on
the co-ordination bond-II:I Infrared spectra of octahedral metal
cyanide complexes. Spectrochim. Acta 1962, 18, 101−103.
(32) Jagner, S.; Ljungstrom, E.; Vannerberg, N. G. The Crystal
Structure of Potassium Hexacyanochromate(III), K3[Cr(CN)6]. Acta
Chem. Scand. 1974, 28a, 623−630.
(33) Entley, W. R.; Treadway, C. R.; Wilson, S. R.; Girolami, G. S.
The Hexacyanotitanate Ion: Synthesis and Crystal Structure of
[NEt4]3[TiIII(CN)6].4MeCN. J. Am. Chem. Soc. 1997, 119, 6251−
6258.
(34) Booth, M. R.; Frankiss, S. G. The constitution, vibrational
spectra and proton resonance of trimethylsilyl cyanide and isocyanide.
Spectrochim. Acta, Part A 1970, 26, 859−869.
(35) Watari, F. Vibrational Spectra and normal coordinate
calculations for (CH3)3GeCN and (CD3)3GeCN. J. Mol. Struct.
1976, 32, 285−295.
(36) Seyferth, D.; Kahlen, N. Trimethyl(iso)cyanogermane and
trimethyltin (iso)cyanide. J. Org. Chem. 1960, 25, 809−812.
(37) Lorberth, J. Preparation of organotin cyanides of the types
R3SnCN and R2Sn(CN)2. Chem. Ber. 1965, 98, 1201−1204.
(38) Arnold, D. E. J.; Cradock, S.; Ebsworth, E. a. V.; Murdoch, J.
D.; Rankin, D. W. H.; Skea, D. C. J.; Harris, R. K.; Kimber, B. J.
Nuclear Magnetic Resonance Spectra of Some Silyl and Trimethylsilyl
Pseudo Halides. J. Chem. Soc., Dalton Trans. 1981, 1349−1351.
(39) Drake, J. E.; Glavincevski, B. M.; Humphries, R. E.; Majid, A.
The carbon-13 chemical shifts of various methylgermanium
derivatives. Can. J. Chem. 1979, 57, 1426−1430.
(40) Brimah, A. K.; Siebel, E.; Fischer, R. D.; Davies, N. A.;
Apperley, D. C.; Harris, R. K. Towards organometallic zeolites:
Spontaneous self-assembly of Et3SnCN, CuCN and (nBu4N)CN to
supramolecular [(nBu4N)(Et3Sn)2Cu(CN)4]. J. Organomet. Chem.
1994, 475, 85−94.
(41) Adamo, C.; Barone, V. Toward reliable density functional
methods without adjustable parameters: The PBE0 model. J. Chem.
Phys. 1999, 110, 6158−6170.
(42) Dunning, T. H., Jr; Peterson, K.; Wilson, A. Gaussian basis sets
for use in correlated molecular calculations. X. The atoms aluminum
through argon revisited. J. Chem. Phys. 2001, 114, 9244.
(43) Peterson, K. A. Systematically convergent basis sets with
relativistic pseudopotentials. I. Correlation consistent basis sets for the
post-d group 13−15 elements. J. Chem. Phys. 2003, 119, 11099−
11112.
(44) Gribov, L. A. The theory of intensities in the infrared spectra of
polyatomic molecules. Pure Appl. Chem. 1969, 18, 339−351.
I
DOI: 10.1021/acs.inorgchem.9b00150
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