Evidence of solubility of the acetylide ion C22-: Syntheses and crystal structures of K2C2·2NH 3, Rb2C2·2NH3, and Cs 2C2·7NH3

Article abstract of DOI:10.1002/anie.201206349

Most alkali- and alkaline-earth-metal acetylides of composition A ₂^IC₂ (A^I=Li-Cs) and (AE)IIC ₂ ((AE)II=Mg-Ba) have been known since the 19th century.[1,2] Very early crystal structure investigations had already revealed that they contA ^In C₂ ^2- dumbbells,[3, 4] but the complex phase behavior of these compounds was elucidated only very recently.[5] In the first half of the last century, CaC₂ in particular, which is accessible from CaO and coal, attracted a lot of interest as an industrial feedstock of acetylene by hydrolysis.[6] Owing to the limited petroleum resources, this reaction has found a revival within the last years.[7] Apart from hydrolysis however, reports on further reactions of alkali- and alkaline-earthmetal acetylides are quite rare, which is surely due in part to the fact that these compounds are insoluble in common solvents.[8] However, during the synthesis of ternary copper acetylides A^ICuC₂ with A^I=K-Cs, we observed that a suspension of A^I 2C₂ in liquid ammonia reacts with CuI at temperatures as low as -78°C within minutes.[9] To clarify whether this reaction can be interpreted as a (low) solubility of A ^I 2C₂ in liquid ammonia, we decided to investigate the system A^I 2C₂/ NH3(l) in more detA^Il. The versatility of liquid ammonia to stabilize unusual mA^In-group-element clusters has been shown by several impressive examples.[10] Herein we report the crystal structures of the ammoniates K2C₂·2NH3 (1), Rb2C₂·2NH3 (2), and Cs2C₂·7NH3 (3),[11a-c] which are the first examples of binary acetylide solvates. Additionally, the crystal structure of [Li(NH3)4]C₂H (4),[11d] which contA ^Ins the hydrogen acetylide anion C₂H-, is briefly presented.

Full text of DOI:10.1002/anie.201206349

.
Angewandte
Communications
DOI: 10.1002/anie.201206349
Acetylide Chemistry
2À
Evidence of Solubility of the Acetylide Ion C2 : Syntheses and Crystal
Structures of K2C2·2NH3, Rb2C2·2NH3, and Cs2C2·7NH3
Markus Hamberger, Stefan Liebig, Ute Friedrich, Nikolaus Korber,* and Uwe Ruschewitz*
Most alkali- and alkaline-earth-metal acetylides of composi-
tion AI2C2 (AI = Li–Cs) and (AE)IIC2 ((AE)II = Mg–Ba) have
been known since the 19th century.[1,2] Very early crystal
structure investigations had already revealed that they con-
ammonia is very much dependent upon the specific synthetic
conditions, such as the corresponding cation, temperature, or
solubility versus precipitation/crystallization. This has already
been reported for the equilibrium between LiC2H and Li2C2,
as upon evaporation of ammonia the LiC2H formed initially
transforms into Li2C2.[24] LiC2H can only be stabilized by
addition of a donor ligand, such as ethylenediamine.[25]
Compounds 1–3 crystallize in the monoclinic space groups
P21/n and C2/m. They exhibit significant differences concern-
ing the coordination spheres of the respective C22À dumbbells
as well as the linkage patterns of the structural units, which
tain C2 dumbbells,[3,4] but the complex phase behavior of
2À
these compounds was elucidated only very recently.[5] In the
first half of the last century, CaC2 in particular, which is
accessible from CaO and coal, attracted a lot of interest as an
industrial feedstock of acetylene by hydrolysis.[6] Owing to the
limited petroleum resources, this reaction has found a revival
within the last years.[7] Apart from hydrolysis however,
reports on further reactions of alkali- and alkaline-earth-
metal acetylides are quite rare, which is surely due in part to
the fact that these compounds are
À
build up the particular crystal structures. The observed C C
bond lengths (listed in Table 1) are slightly elongated
insoluble in common solvents.[8]
Table 1: Space groups and selected interatomic distances for K2C2·2NH3, Rb2C2·2NH3, and Cs2C2·7NH3.
However, during the synthesis of
ternary copper acetylides AICuC2
with AI = K–Cs, we observed that
a suspension of AI2C2 in liquid
ammonia reacts with CuI at tem-
peratures as low as À788C within
minutes.[9] To clarify whether this
Compound
C C [ꢀ]
C-AI [ꢀ] (AI =K–Cs)
C···H [ꢀ]
Space group
À
K2C2·2NH3
Rb2C2·2NH3
Cs2C2·7NH3
1.241(3)
1.238(12), 1.238(11)
1.21(2)
2.994(2)–3.339(2)
3.248(3)–3.460(4)
3.444(5)–3.538(6)
2.34(2), 2.53(3)
2.31(5)–2.44(8)
2.30(8)–2.48(4)
P21/n
C2/m
C2/m
reaction can be interpreted as a (low) solubility of AI2C2 in
liquid ammonia, we decided to investigate the system AI2C2/
NH3(l) in more detail. The versatility of liquid ammonia to
stabilize unusual main-group-element clusters has been
shown by several impressive examples.[10] Herein we report
the crystal structures of the ammoniates K2C2·2NH3 (1),
Rb2C2·2NH3 (2), and Cs2C2·7NH3 (3),[11a–c] which are the first
examples of binary acetylide solvates. Additionally, the
crystal structure of [Li(NH3)4]C2H (4),[11d] which contains
the hydrogen acetylide anion C2HÀ, is briefly presented.
Single crystals of 1–4 crystallized from suspensions of
AI2C2 (AI = Li, K–Cs) in liquid ammonia at temperatures
below À408C (see the Experimental Section). The observa-
compared to the expected value for a C C triple bond as
obtained from previous experimental data (acetylene
1.205 ꢀ,[12] K2C2 1.19(1) ꢀ,[5b] CaC2 1.191 ꢀ[13]). This diver-
gence is surprising at first sight, but in several theoretical
À
À
investigations, C C distances ranging from 1.254 ꢀ to 1.264 ꢀ
were calculated for Rb2C2,[14] Cs2C2,[14] and CaC2.[15] It should
be further noted that most experimental data were obtained
from measurements recorded at ambient conditions. Thus,
a dynamic disorder of the C22À dumbbells around their center
of gravity is likely,[16] which would reduce the C C distances
À
À
determined by diffraction. Accordingly, the “real” C C
distance within an alkali- or alkaline-earth-metal acetylide
is somewhat ambiguous. Interestingly, in a neutron diffraction
experiment on BaC2 at 20 K we obtained a C C distance of
1.243(3) ꢀ, but the quality of the data and the resulting
2À
tion that compounds containing C2 or C2HÀ anions are
À
obtained under very similar synthetic conditions points to the
fact that the equilibrium between C2 and C2HÀ in liquid
refinement was only modest.[5g]
2À
Herein we present the results of low-temperature inves-
tigations (T= 123(2) K), so that the dynamic disorder of the
C2 dumbbells can be assumed to be almost frozen. Similar
[*] M. Hamberger,[+] U. Friedrich, Prof. Dr. N. Korber
Institut fꢁr Anorganische Chemie, Universitꢂt Regensburg
Universitꢂtsstrasse 31, 93040 Regensburg (Germany)
E-mail: nikolaus.korber@chemie.uni-regensburg.de
À
slightly enhanced C C distances were obtained by other
II
ꢀ
authors on acetylides of composition (AE) (C CR)2 with
(AE)II = Ca–Ba and R = organic substituent.[17] Other struc-
S. Liebig,[+] Prof. Dr. U. Ruschewitz
Institut fꢁr Anorganische Chemie, Universitꢂt zu Kçln
Greinstrasse 6, 50939 Kçln (Germany)
E-mail: uwe.ruschewitz@uni-koeln.de
ture-dependent effects, which might also affect the (different)
À
C C distances within 1–3, will be discussed below.
The anion in K2C2·2NH3 (1) is coordinated by six
potassium cations, leading to a heavily distorted octahedral
environment (coordination number CN = 6; see Figure 1a).
In contrast, the two acetylide ions in Rb2C2·2NH3 (2)
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201206349.
13006
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 13006 –13010

Angewandte
Chemie
À
slightly elongated C C distances within the C2 dumbbells, as
they remove electron density from the anions. Additionally,
À
the C C bond lengths of 1–3 slightly decrease from
1.241(3) ꢀ for the potassium to 1.21(2) ꢀ for the cesium
compound. But in the case of Cs2C2·7NH3 (3), slightly
enlarged anisotropic displacement parameters of the carbon
atoms are found, pointing to a librational disorder, which
À
should reduce the apparent C C distance.
The linkage of the (C2)AIn polyhedra (n = 4, 6, 8)
described above and the associated formation of the ammo-
nia-containing crystal structures are quite different for 1–3.
2À
As shown in Figure 2a, K2C2·2NH3 (1) consists of C2
-
centered K6 octahedra, which are edge-linked to form layers
being separated by ammonia molecules. This two-dimen-
Figure 1. a) Crystal structure of K2C2·2NH3. The distorted octahedral
2À
coordination sphere around one C2 dumbbell is shaded. The
coordination sphere around one K+ cation is also emphasized.
b) Crystal structure of Rb2C2·2NH3 with a square-prismatic and
2À
a square-planar Rb coordination around two C2 dumbbells, respec-
tively. Ellipsoids are set at 70% probability.
(Figure 1b), which are in each case generated by one
crystallographically independent carbon atom, are sur-
rounded by eight and four rubidium cations respectively,
yielding a slightly distorted cubic (CN = 8) and a square-
planar coordination sphere (CN = 4). In a similar manner, the
2À
C2 dumbbell in the asymmetric unit of Cs2C2·7NH3 (3) is
located in a square-planar Cs coordination sphere (CN = 4).
These coordination spheres are completed by contacts to NH3
I
À
molecules. The C A distances in 1–3 (Table 1) are in good
agreement with the corresponding distances in the binary
acetylides K2C2 (3.009(5)–3.146(3) ꢀ),[5b] Rb2C2 (3.107(4)–
3.447(6) ꢀ),[5d] Cs2C2 (3.21(3)–3.65(2) ꢀ),[5d] and in the hydro-
gen acetylide ammoniates K2Zn(C2H)4·2NH3 (2.997(3)–
3.291(3) ꢀ) and K2Cd(C2H)4·2NH3 (3.023(3)–3.375(4) ꢀ).[18]
It is not entirely surprising that the C···H distances
Figure 2. a) Two-dimensional layers assembled from edge-linked (C2)K6
octahedra (emphasized in gray) in K2C2·2NH3 (1). These layers are
separated by ammonia molecules. b) Rb2C2·2NH3 (2): three-dimen-
sional network built up from layers of edge-linked (C2)Rb8 cubes
connected by vertices with strands of planar edge-linked (C2)Rb4 units
(shaded parts of the picture) to form channels filled with NH3
molecules. c) One-dimensional strands of edge-linked planar (C2)Cs4
units running parallel to the b axis in the ammonia-rich Cs2C2·7NH3
(3). These strands are completely separated from each other by NH3
molecules. In (c) the isotropically refined N4 atom is shown without
its H atoms. Ellipsoids are set at 50% probability.
2À
between C2 and NH3 (Table 1) in each of the three
presented compounds are significantly shorter than the sum
of the van der Waals radii,[19] so that moderate to weak
hydrogen bonds have to be taken into account. Consequently,
2À
the coordination spheres of the C2 ions can be enlarged to
(C2)K6(NH3)4 (CN = 6 + 4), (C2)Rb8(NH3)4/(C2)Rb4(NH3)8
(CN = 8 + 4/4 + 8), and (C2)Cs4(NH3)8 (CN = 4 + 8). These
À
C···H N hydrogen bonds might also be responsible for the
Angew. Chem. Int. Ed. 2012, 51, 13006 –13010
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 13007

.
Angewandte
Communications
sional part of 1 can be understood as a distorted variant of the
layers in the CdI2 type structure (see the Supporting
Information, Figure S1).
In contrast, Rb2C2·2NH3 (2) forms a three-dimensional
network built from layers of (C2)Rb8 cubes linked among each
other by six of their eight vertices. The remaining two vertices
of each cube are further connected with strands of almost
planar (C2)Rb4 units, which are linked by common edges
among each other (Figure 2b). The resulting channels are
filled with NH3 molecules (Supporting Information, Fig-
ure S2). The characteristic structural motifs of the ammonia-
rich compound Cs2C2·7NH3 (3) are one-dimensionally
extended, completely isolated strands of edge-linked
(C2)Cs4 units that are surrounded by ammonia (Figure 2c).
It is evident that, particularly with regard to the isostructural
binary acetylides Rb2C2 and Cs2C2,[5d] the acetylide ammoni-
ates of these alkali-metal cations display a wide structural
variability, which is a consequence of a varying ammonia
content as well as the role of ammonia as a cation-coordinat-
ing dipole and a hydrogen-bond donor.
Figure 3. Crystal structure of [Li(NH3)4]C2H (4). The formally negatively
charged carbon atom builds up square-pyramidally aligned hydrogen
bonds with the [Li(NH3)4]+ complexes. The H atom of the C2HÀ anion
isolates the two-dimensional layers which run along the (001) plane
against each other. Ellipsoids are set at 50% probability.
The solubility of acetylene in liquid ammonia solution is
well-investigated.[20] The addition of alkali metals to this
solution leads to solvated hydrogenacetylide ions C2HÀ.[1a–d]
However, prior to our work it seemed very unlikely that the
C22À ion can also be stable in any protic solvent because of its
high charge and small size. Only few examples for similar
highly charged anions in solution have been reported, for
example Sn44À, Pb44À [21] and Sb88À [22] For these species liquid
, .
ammonia constitutes a well-suited medium owing to the fact
that oxidation by protons is kinetically unfavorable.[23]
Thus, while the alkali-metal hydrogenacetylides AIC2H
(AI = Na–Cs) are routinely synthesized in liquid ammonia[1a–d]
(see also the Experimental Section), the alkali metal acety-
lides AI2C2 have only been accessible by high-temperature
routes.[1a,b,5b,d,24] With the preparation of K2C2·2NH3,
Rb2C2·2NH3, and Cs2C2·7NH3 from the corresponding
binary acetylides in liquid ammonia, we now show that the
Scheme 1. Postulated equilibrium of the three solvated species C2H2,
2À
C2HÀ, and C2 in liquid ammonia. Either a stoichiometric amount of
alkali metal is added to an ammonia–acetylene solution, resulting
initially in C2HÀ, or binary acetylides AI2C2 (with AI =Li, K–Cs) are
dissolved in NH3(l), initially resulting in C22À. Evaporation of the
solvent leads to the precipitation of the alkali-metal hydrogen acety-
lides AIC2H (AI =Na–Cs) or Li2C2. At low temperatures, the slow
crystallization of 1–4 is observed.
2À
C2 anion is also solvated in NH3 in sufficient quantities to
form crystals of 1–3.
Furthermore, the following conclusion can be drawn from
these observations: in liquid ammonia, the acetylene mole-
cule C2H2 (pKS ꢁ 25), the hydrogenacetylide ion C2HÀ, and
crystallizes. At À408C, however, the obviously lower solubil-
ity of the acetylide ammoniates 1–3 prevails, thus leading to
the crystallization of these compounds.
2À
the acetylide ion C2 most likely exist in equilibrium. This
assumption is strongly supported by the fact that it was
possible to obtain the novel hydrogen acetylide compound
[Li(NH3)4]C2H (4) by dissolution and protonation of Li2C2.
As mentioned earlier, LiC2H transforms to Li2C2 upon
evaporation of ammonia.[24] Here, at lower temperatures the
ammoniate of LiC2H is crystallized, which strongly corrobo-
Therefore, it seems conceivable that under certain con-
ditions, alkali-metal acetylides or even alkaline-earth-metal
acetylides can be prepared from solution. This is an important
step towards the preparation of new carbides from solution.
Furthermore, it opens the door for a novel acetylide chemistry
in solution.
In summary, we have been able to synthesize the first
solvates of binary acetylides (AI = K–Cs) and characterize
them by single-crystal X-ray diffraction. To our knowledge,
they further constitute the only examples of single-crystal
studies of binary alkali-metal acetylides at all. But most
importantly, they give the first evidence of a solubility of the
C22À anion in any solvent. Li2C2 was also successfully dissolved
in liquid ammonia to give a hydrogen acetylide ammoniate.
Further investigations concerning the alkaline-earth-metal
acetylides, NMR experiments of the acetylide–ammonia
2À
rates the proposed equilibrium between C2 and C2HÀ.
Furthermore, the crystal structure of 4 contains the first
example of a C2HÀ anion without any metal contacts
(Figure 3). Scheme 1 illustrates the proposed equilibrium
between C2H2, C2HÀ, and C22À. The equilibrium lies mainly on
the side of C2HÀ, as upon evaporation of the solvent AIC2H
precipitates for AI = Na–Cs, so that the equilibrium is shifted
even more to the side of C2HÀ. For AI = Li however, the
opposite behavior is found, as upon evaporation of ammonia
Li2C2 is formed and at lower temperatures [Li(NH3)4]C2H (4)
13008 www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 13006 –13010

Angewandte
Chemie
Marzini, H. A. Mayer, H.-J. Meyer, Z. Anorg. Allg. Chem. 2001,
solutions, and experiments on the reactivity of the dissolved
C22À anions are under way.
627, 1090; i) U. Ruschewitz, Coord. Chem. Rev. 2003, 244, 115.
[6] J. T. Morehead, G. De Chalmot, J. Am. Chem. Soc. 1896, 18, 311.
[7] a) G. Li, Q. Liu, Z. Liu, Z. C. Zhang, C. Li, W. Wu, Angew.
Chem. 2010, 122, 8658; Angew. Chem. Int. Ed. 2010, 49, 8480;
b) http://www.busytrade.com/news/newsinfo.php?id = 2425.
[8] a) W. A. Barber, C. L. Sloan, J. Phys. Chem. 1961, 65, 2026;
b) A. C. Matignon, C. R. Hebd. Seances Acad. Sci. 1897, 125,
1034.
Experimental Section
All of the preparations were carried out under an inert argon
atmosphere using Schlenk and glove-box techniques. NH3 (Linde)
was dried by distillation from sodium and it was stored at À788C. The
acetylides K2C2, Rb2C2, and Cs2C2 were prepared according to the
known procedures.[5b,d]
[9] U. Cremer, W. Kockelmann, M. Bertmer, U. Ruschewitz, Solid
State Sci. 2002, 4, 247.
Li2C2: Stoichiometric amounts of lithium and graphite were
heated for 24 h at 1073 K in a sealed Ta ampoule.
[10] a) S. Scharfe, F. Kraus, S. Stegmaier, A. Schier, T. F. Fꢃssler,
Angew. Chem. 2011, 123, 3712; Angew. Chem. Int. Ed. 2011, 50,
3630; b) S. Joseph, M. Hamberger, F. Mutzbauer, O. Hꢃrtl, M.
Meier, N. Korber, Angew. Chem. 2009, 121, 8926; Angew. Chem.
Int. Ed. 2009, 48, 8770.
K2C2·2NH3, Rb2C2·2NH3, Cs2C2·7NH3, [Li(NH3)4]C2H: K2C2
(0.051 g, 0.50 mmol) was filled into a vacuum-dried Schlenk tube
and dried ammonia (ca. 20 mL) was condensed at À788C. For Rb2C2
(0.066 g, 0.34 mmol), Cs2C2 (0.12 g, 0.41 mmol), and Li2C2 (0.250 g,
6.60 mmol), the same procedure was applied. The respective reaction
vessels with suspensions of black solids in colorless liquids were first
stored at À408C for several weeks and afterwards concentrated and
stored at À758C to induce crystallization.
[11] a) Structure refinement of K2C2·2NH3: C2H6K2N2, Mr =
136.29 gmolÀ1, crystal size 0.30 ꢄ 0.25 ꢄ 0.20 mm3, monoclinic,
space group P21/n, a = 7.1658(13), b = 5.5810(14), c =
8.3330(15) ꢀ, b = 113.881(13)8, V= 304.73(11) ꢀ3, Z = 2,
1calcd = 1.485 MgmÀ3, m(MoKa) = 1.422 mmÀ1, T= 123(2) K, q =
3.18–26.488, measured/independent/observed (I > 2s(I)) reflec-
tions 4392/605/534, Rint = 0.0299, R (F) (all data) = 0.0231, wR
(F2) (all data) = 0.0478, max./min. residual electron density:
0.212/À0.172 eꢀÀ3; b) Structure refinement of Rb2C2·2NH3:
For X-ray investigations, the thermally unstable, air- and mois-
ture-sensitive colorless crystals of K2C2·2NH3, Rb2C2·2NH3,
Cs2C2·7NH3, and [Li(NH3)4]C2H were isolated from the mother
liquor and directly transferred into a perfluoroether oil, which was
cooled under a N2 stream. By the use of the crystal-cap system the
crystals were mounted onto a STOE-IPDS I diffractometer, where
the data collection was performed at 123(2) K using graphite-
monochromated MoKa radiation (l = 0.71073 ꢀ). The data reduction
was carried out with the STOE program package.[26] The structures
were solved by direct methods using SHELXS-97.[27]
C2H6Rb2N2, Mr = 229.02 gmolÀ1
,
crystal size 0.20 ꢄ 0.20 ꢄ
0.05 mm3, monoclinic, space group C2/m, a = 10.864(2), b =
4.9543(10), c = 11.568(2) ꢀ, b = 99.93(3)8, V= 613.3(2) ꢀ3, Z =
4, 1calcd = 2.480 MgmÀ3, m(MoKa) = 15.827 mmÀ1, T= 123(2) K,
q = 3.81–26.508, measured/independent/observed (I > 2s(I))
reflections 4381/664/582, Rint = 0.0472, R (F) (all data) = 0.0308,
wR (F2) (all data) = 0.0655, max./min. residual electron density:
More details are given in the Supporting Information.
0.716/À0.813 eꢀÀ3
; c) Structure refinement of Cs2C2·7NH3:
Received: August 7, 2012
Published online: November 19, 2012
C2H21Cs2N7, Mr = 409.01 gmolÀ1
,
crystal size 0.25 ꢄ 0.20 ꢄ
0.1 mm3, monoclinic, space group C2/m, a = 11.396(3), b =
5.0728(8), c = 11.184(2) ꢀ, b = 90.052(18)8, V= 646.5(2) ꢀ3,
1calcd = 2.096 MgmÀ3
,
m(MoKa) = 5.609 mmÀ1
,
T=
Keywords: acetylides · alkali metals · ammoniates ·
Z = 2,
.
crystal structure · solubility
123(2) K, q = 3.58–28.078, measured/independent/observed (I >
2s(I)) reflections 819/819/743, Rint = 0.0414, R (F) (all data) =
0.0351, wR (F2) (all data) = 0.1006, max./min. residual electron
density: 2.251/À0.884 eꢀÀ3; d) Structure refinement of [Li-
(NH3)4]C2H: C2H4Li1N1, Mr = 100.09 gmolÀ1, crystal size 0.1 ꢄ
0.1 ꢄ 0.1 mm3, tetragonal, space group P4/n, a = 8.4019(12), c =
5.041(1) ꢀ, V= 355.85(10) ꢀ3, Z = 2, 1calcd = 0.943 MgmÀ3, m-
(MoKa) = 0.063 mmÀ1, T= 123(2) K, q = 3.43 – 25.398, measured/
[1] a) M. H. Moissan, C. R. Hebd. Seances Acad. Sci. 1898, 126, 302;
b) M. H. Moissan, C. R. Hebd. Seances Acad. Sci. 1898, 127, 911;
c) M. H. Moissan, C. R. Hebd. Seances Acad. Sci. 1903, 136, 1217;
d) M. H. Moissan, Bulll. Soc. Chim. Fr. 1904, 31, 511; e) R. Juza,
V. Wehle, H.-U. Schuster, Z. Anorg. Allg. Chem. 1965, 352, 252.
[2] a) J. Novꢁk, Z. Phys. Chem. 1910, 73, 513; b) C. Winkler, Ber.
Dtsch. Chem. Ges. 1890, 23, 2642; c) L. Maquenne, C. R. Hebd.
Seances Acad. Sci. 1892, 115, 558; d) M. H. Moissan, C. R. Hebd.
Seances Acad. Sci. 1894, 118, 684.
[3] a) R. Juza, V. Wehle, H.-U. Schuster, Z. Anorg. Allg. Chem.
1965, 352, 252; b) R. Juza, V. Wehle, Naturwissenschaften 1965,
52, 537; c) H. Fçppl, Angew. Chem. 1958, 70, 401; d) M. Atoji, J.
Chem. Phys. 1974, 60, 3324.
[4] a) P. Karen, A. Kjekshus, Q. Huang, V. L. Karen, J. Alloys
Compd. 1999, 282, 72; b) M. von Stackelberg, Naturwissenschaf-
ten 1930, 18, 305; c) M. von Stackelberg, Z. Phys. Chem. Abt. B
1930, 9, 437; d) M. Atoji, R. C. Medrud, J. Chem. Phys. 1959, 31,
332.
[5] a) U. Ruschewitz, R. Pçttgen, Z. Anorg. Allg. Chem. 1999, 625,
1599; b) S. Hemmersbach, B. Zibrowius, U. Ruschewitz, Z.
Anorg. Allg. Chem. 1999, 625, 1440; c) K.-H. Klçss, D. Hinz-
Hꢂbner, U. Ruschewitz, Z. Anorg. Allg. Chem. 2002, 628, 2701;
d) U. Ruschewitz, P. Mꢂller, W. Kockelmann, Z. Anorg. Allg.
Chem. 2001, 627, 513; e) M. Knapp, U. Ruschewitz, Chem. Eur. J.
2001, 7, 874; f) V. Vohn, M. Knapp, U. Ruschewitz, J. Solid State
Chem. 2000, 151, 111; g) V. Vohn, W. Kockelmann, U. Rusche-
witz, J. Alloys Compd. 1999, 284, 132; h) J. Glaser, S. Dill, M.
independent/observed (I > 2s(I)) reflections 2172/330/226, Rint
=
0.1888, R (F) (all data) = 0.0773, wR (F2) (all data) = 0.1446,
max./min. residual electron density: 0.16/À0.15 eꢀÀ3. For a brief
description of the data collection and the solution and refine-
ment of the structures see Experimental Section. Further details
on the crystal structure investigation may be obtained from the
Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leo-
poldshafen, Germany (fax: (+ 49)7247-808-666; e-mail: crysda-
ta@fiz-karlsruhe.de), on quoting the depository numbers CSD
425116, 425117, 425118, and 425119.
[12] G. Herzberg, J. W. T. Spinks, Z. Phys. 1934, 91, 386.
[13] M. Atoji, J. Chem. Phys. 1961, 35, 1950.
[14] B. Winkler, V. Milman, Solid State Commun. 2002, 121, 155.
[15] P. Zaleski-Ejgierd, M. Hakala, P. Pyykkç, Phys. Rev. B 2007, 76,
094104.
[16] B. Zibrowius, C. Bꢃhtz, M. Knapp, U. Ruschewitz, Phys. Chem.
Chem. Phys. 2004, 6, 5237.
[17] M. A. Guino-o, J. S. Alexander, M. L. McKee, H. Hope, U. B.
Englich, K. Ruhlandt-Senge, Chem. Eur. J. 2009, 15, 11842.
[18] U. Cremer, I. Pantenburg, U. Ruschewitz, Inorg. Chem. 2003, 42,
7716.
[19] A. Bondi, J. Phys. Chem. 1964, 68, 441.
Angew. Chem. Int. Ed. 2012, 51, 13006 –13010
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 13009

.
Angewandte
Communications
[20] R. J. Tedeschi, A. W. Casey, G. S. Clark Jr. , R. W. Huckel, L. M.
Kindley, J. P. Russell, J. Org. Chem. 1963, 28, 1740.
[21] K. Wiesler, K. Brandl, A. Fleischmann, N. Korber, Z. Anorg.
Allg. Chem. 2009, 635, 508.
[24] M. Corbellini, L. Turner, Chim. Ind. 1960, 42, 251.
[25] O. F. Beumel, Jr., R. F. Harris, J. Org. Chem. 1963, 28, 2775.
[26] STOE & Cie GmbH, STOE X-Area Program Package, Darm-
stadt, Germany, 2005.
[22] M. Reil, N. Korber, Z. Anorg. Allg. Chem. 2007, 633, 1599.
[23] Chemistry in Nonaqueos Ionizing Solvents, Vol. I (Eds.: G.
Jander, H. Spandau, C. C. Addison), Vieweg, Braunschweig,
1966, pp. 381 – 427.
[27] SHELXS-97: G. M. Sheldrick, University of Gçttingen, 1997.
13010 www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 13006 –13010