Donor-acceptor complexes of tellurium polycatlonlc clusters with cyanogen

Article abstract of DOI:10.1002/zaac.200801422

The reactions of cyanogen with Te₆[AsF₆]₄ and Te₄[AsF₆]₂ in SO₂ solutions yield Te₆[AsF₆]₄.1.5C₂N₂ (1) and Te₄[A

Full text of DOI:10.1002/zaac.200801422

ARTICLE
DOI: 10.1002/zaac.200801422
Donor-Acceptor Complexes of Tellurium Polycationic Clusters with Cyanogen
Johannes Beck*[a] and Marcus Zink[a]
Dedicated to Professor Reinhard Nesper on the Occasion of His 60th Birthday
Keywords: Cyanogen; Sulfur Dioxide; Tellurium; Hexafluorido arsenate(V); Raman spectroscopy
4ϩ
Abstract. The reactions of cyanogen with Te6[AsF6]4 and
Te4[AsF6]2 in SO2 solutions yield Te6[AsF6]4 ·1.5C2N2 (1) and
Te4[AsF6]2 ·C2N2 (2) as red crystals in quantitative yield. The com-
plexes 1 and 2 are also generated in moderate yield by the reaction
of Te, AsF5 and C2N2 in liquid SO2, but by-products are formed.
These reactions show the ability of cyanogen to act as a donor
towards tellurium polycations. In the crystal structures, discrete
octahedral [AsF6]Ϫ ions are present and linear cyanogen molecules,
which coordinate the tellurium atoms of the polycations η2 by both
nitrogen atoms. In the crystal structure of 1, the trigonal-prismatic
Te6 clusters are bridged by cyanogen molecules to one-dimen-
sional zig-zag chains. The crystal structure of 2 contains square-
planar Te4 clusters, which are bridged by cyanogen molecules to
2ϩ
two-dimensional sheets. The complexes 1 and 2 represent the first
chalcogen polycationic cluster compounds containing a nitrogen
ligation. The new compounds are unstable with respect to loss of
cyanogen but stable under an atmosphere of C2N2. The Raman
spectra of 1 and 2 were investigated and assigned. A serviceable
and convenient way to handle air-sensitive and cold liquids by a
transfer needle technique is described.
Te4[AsF6]2 ·SO2 [6] and Te6[AsF6]4 ·2SO2 [7]. Here, the SO2
molecules are coordinated with their oxygen atoms to the
cationic clusters and act either as terminal μ1-ligands or
bridge the edges as μ2-ligands.
Introduction
The formation of polycationic clusters of various size,
shape, and charge is a well-known feature of the elements
of the chalcogen series, of which tellurium has the richest
structural chemistry [1]. The highly electrophilic chalcogen
polycations are prepared by three main synthetic routes: in
acidic melts [2], in solution, e.g. liquid SO2, AsF3, benzene
[3] or super acidic solutions e.g. HF/AsF5 [4], and in chemi-
cal vapor transport reactions using volatile metal halides as
oxidants towards elemental chalcogens [5]. By all three
routes ionic compounds are obtained, whose anions, as
weak conjugate bases of strong Lewis acids, stabilize the
“naked” polycationic clusters. The most common and
straight forward possibility to transform elemental tel-
lurium to cationic clusters is the use of MF5 (M ϭ As, Sb)
as two electron oxidizing agents. The reduction to MF3
liberates FϪ ions, which generate with MF5 the weakly
coordinating [MF6]Ϫ ions, representing suitable, weakly
basic counterions. Liquid SO2 is a convenient solvent for
reactions of this kind. It is inert against AsF5 und dissolves
tellurium polycations without decomposition. It has weakly
basic properties, since generally SO2 containing crystals
are isolated from its solutions with SO2 coordinating
the cationic clusters. Examples are the structures of
To the best of our knowledge, no polycationic cluster
compounds containing a ligation by a nitrogen donor are
known. Cyanogen, NCϪCN, has some properties, which
make it a solvent similar to SO2. It has a boiling point of
Ϫ21 °C (SO2 Ϫ10 °C) and can thus be handled at ambient
temperature with a vapor pressure of about 3 bar. It has
two weak nucleophilic centers at the terminal nitrogen
atoms and is able to act as a σ-donor ligand. Only six
structurally characterized coordination compounds of
cyanogen are presented in the literature. Two of them are
based on antimony pentahalides, SbCl5 ·NCCN·SbCl5
and SbF5 ·NCCN [8], the others on transition metals,
{[Ag(NCCN)2][AsF6]}n [9], [Cd[AsF6]2(NCCN)2(SO2)]n
[10],
trans-[Ni(CN)2(PPh3)2]·(C2N2)2
[11]
and
[Zn(NCCN)6][AsF6]2 [12].
We conducted experiments for the oxidation of elemental
tellurium by AsF5 in liquid C2N2 and in C2N2/SO2 mixtures
to explore the usability of cyanogen as a solvent for such
reactions and to probe for its coordination abilities towards
the polycationic clusters. We found that C2N2 is suitable as
a new solvent and acts as a new coordinating ligand
4ϩ
towards the tellurium clusters Te6 and Te42ϩ, what about
we report in the following.
* Prof. Dr. J. Beck
E-Mail: j.beck@uni-bonn.de
[a] Institut für Anorganische Chemie
Universität Bonn
Experimental Section
Caution: Cyanogen is severely poisonous, having a toxicity compar-
Gerhard-Domagk-Str. 1
53121 Bonn, Germany
able to that of hydrogen cyanide. The maximum tolerable vapor
692
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2009, 635, 692Ϫ699

Donor-Acceptor Complexes of Tellurium Polycationic Clusters with Cyanogen
concentration is 10 parts per million [13]. Cyanogen is highly in-
flammable and burns in air generating temperatures up to 5000 °C.
AsF5 is also highly toxic, liberating HF and As2O5 on contact with
humid air. All experiments have to be carried out in a well venti-
lated hood.
Te4[AsF6]2 ·SO2 (3)
Finely powdered tellurium (500 mg, 3.92 mmol) was loaded in an
argon filled glove-box into the evacuated arm of an H-shaped ves-
sel. AsF5 (520 mg, 3.06 mmol) and anhydrous SO2 (40 mL) were
condensed onto the tellurium using a cooling bath (Ϫ140 °C). The
reactants were stirred at Ϫ30 °C for 2 h and afterwards for 5 h at
20 °C. The dark red solution containing Te4[AsF6]2 was filtered to
the other side of the H-shaped vessel and the volatiles SO2 and
AsF5 were distilled back to the other side onto the remaining
amount of tellurium to complete the reaction. The formed light red
solution was filtered again and combined with the red precipitate
of (3) in the second compartment. The solvent was concentrated
and decanted by a stainless steel cannula yielding a red powder
together with a large number of red crystals. The Raman spectra
of the red solids were in full agreement with the spectra reported
for Te4[AsF6]2 [6]. The compound was dissolved and stored in an-
hydrous sulfur dioxide (40 mL).
For all reactions, pressure stable “H-shaped” thick walled glass
Schlenk tubes (diameter 2 cm, volume 2 ϫ 40 mL) equipped with
two screw plug valves made of PTFE [14] and a medium porosity
glass frit between the two compartments were used. All glass equip-
ment (Simax® glass) was preheated two times under vacuum to
remove adsorbed moisture (approx. 350 °C / 3 ϫ 10Ϫ3 mbar).
Tellurium was purified by sublimation at 350 °C under vacuum to
remove TeO2 and traces of TeO3, which are not volatile under these
conditions. Cyanogen was prepared in an all-glass vacuum line by
pyrolysis of silver cyanide, which had itself been prepared from
potassium cyanide and silver nitrate [15]. It was stored over P4O10
and freshly distilled before use. The melting and boiling points of
cyanogen are Ϫ28 °C and Ϫ21 °C, respectively [16]. The desired
amount of C2N2 was added into the reaction vessels using a vac-
uum line of calibrated volume or from a calibrated vessel using a
stainless steel cannula. Liquid SO2 was dried by storing over P4O10
and was freshly distilled into the reaction vessel for each experi-
ment. Solutions of Te4[AsF6]2 and Te6[AsF6]4 are stable in liquid
SO2 and can be stored in glass vessels over years. For all reactions
a cannula transfer technique was used to transfer the liquid SO2
solutions of Te4[AsF6]2 and Te6[AsF6]4 at approximate Ϫ70 °C
from a calibrated H-tube vessel to the reaction vessel kept at
Ϫ140 °C. The technical layout of the apparatus is described in Fig-
ure 1. Since all investigated compounds are very sensitive towards
loss of the volatile C2N2, samples were left inside the reaction vessel
covered with some liquid SO2 or liquid cyanogen or were kept un-
der a SO2/C2N2 gas atmosphere.
Te6[AsF6]4 ·2SO2 (4)
Analogously to the synthesis of 3, tellurium (70.4 mg, 0.550 mmol),
a 10-fold excess of AsF5 (920 mg, 5.50 mmol) and liquid SO2
(40 mL) were used. On warming the mixture to room temperature
2ϩ
and stirring, a deep red color, caused by the emergence of the Te4
cation appeared, which changed to red-brown after one hour. After
two days, this solution was filtered through the glass frit into the
second compartment of the reaction vessel and left standing for
two weeks. The solution gained finally a light orange-brown color
and some dark red crystals precipitated when the solvent volume
was reduced in vacuo until crystallization started. After standing
an additional week, large dark red crystals settled and the color of
the solution turned yellow-red. Afterwards, the solvent was concen-
trated and decanted by the stainless steel cannula technique. The
Raman spectrum of the solid was in agreement with literature data
for Te6[AsF6]4 ·2SO2 [7]. Dark red, prismatic crystals of 4 were iso-
lated and stored in anhydrous SO2 (40 mL). Because 4 has an in-
verse temperature gradient of the solubility in liquid SO2, the solu-
tion must be stirred at Ϫ70 °C for two minutes before transferring
by cannula from the calibrated vessel.
Te6[AsF6]4 ·1.5C2N2 (1)
In a typical experiment a freshly prepared solution of 4 (20 mL),
cooled to Ϫ70 °C, was added through a stainless steel cannula, by
applying an argon pressure gradient, onto a frozen mixture of
cyanogen (3 mL, 54.8 mmol) and SO2 (15 mL) kept at Ϫ140 °C,
using the technique described in Figure 1. The red solution was
stirred at Ϫ30 °C for 1 h and afterwards another hour at 20 °C.
Subsequently, the solvent volume was reduced to one third of its
original volume by distillation. Keeping the concentrated red
solution by a water bath at 20 °C, red crystals of 1 deposited in
quantitative yield. Raman spectra of the solid, taken from different
regions of the solid material showed only the presence of 1.
Figure 1. Technical layout of the apparatus to transfer the cold
liquid SO2, liquid cyanogen, or solutions of Te4[AsF6]2 or
Te6[AsF6]4 into SO2/C2N2 mixtures under anhydrous conditions
between “H-shaped” glass vessels. Explanation: 1) Stainless steel
cannula. The ends of the stainless steel cannula are pointed, so they
can be inserted through the septa. 2) PTFE high vacuum screw
plug valve [14] 3) H-shaped thick-walled glass flask with two valves
and a medium porosity glass frit between the two compartments
4) Teflon valve substituted by a septum 5) Penetrated septum by a
stainless steel needle for argon pressure compensation 6) Cooling
bath 7) Solution of Te4[AsF6]2 or Te6[AsF6]4 in liquid SO2 8)
Solvent composed of mixture of liquid SO2/C2N2.
Te4[AsF6]2 ·C2N2 (2)
In a typical experiment as described in Figure 1, a freshly prepared
solution of 3 (20 mL), cooled to Ϫ70 °C, was added by a stainless
steel cannula onto a frozen mixture of (3 mL, 54.8 mmol) cyanogen
and SO2 (15 mL) at Ϫ140 °C. The red solution was stirred at
Ϫ30 °C for 1 h and subsequently another hour at 20 °C. After-
Z. Anorg. Allg. Chem. 2009, 692Ϫ699
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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693

J. Beck, M. Zink
ARTICLE
Table 1. Crystallographic data and details of the structure refine-
Table 2. Atomic coordinates (ϫ 104) and equivalent isotropic
2
3
˚
ment for Te6[AsF6]4 ·1.5C2N2 and Te4[AsF6]2 ·C2N2. Standard displacement parameters /A ϫ 10 for Te6[AsF6]4 ·1.5C2N2 (1).
deviations given in brackets refer to the last significant digit.
Ueq is defined as one third of the trace of the orthogonalized Uij
tensor.
Formula
Te6[AsF6]4 ·1.5C2N2 Te4[AsF6]2 ·C2N2
x
y
z
Ueq
Crystal system
Space group
Lattice constants /A
monoclinic
C2/m
monoclinic
P21/n
Te(1)
Te(2)
Te(3)
As(1)
As(2)
As(3)
As(4)
As(5)
F(1)
F(2)
F(3)
F(4)
F(5)
F(6)
F(7)
F(8)
F(9)
F(10)
F(11)
F(12)
F(13)
F(14)
F(15)
F(16)
F(17)
C(1)
6743(1)
8477(1)
6871(1)
4086(1)
5000
17(1)
5000
1358(1)
4969(3)
3268(3)
4749(2)
3475(2)
1761(3)
992(3)
2179(2)
525(2)
109(3)
Ϫ1201(3)
1231(3)
Ϫ88(3)
5780(4)
4031(3)
5000
5739(3)
4300(2)
Ϫ488(6)
1303(6)
7473(4)
7405(4)
1588(1)
1605(1)
1605(1)
0
0
0
0
0
3520(1)
3295(1)
2161(1)
2423(1)
5000
1992(1)
0
4550(1)
2000(2)
2891(3)
3015(2)
1881(2)
3818(2)
5314(2)
4935(2)
4176(2)
2643(2)
1863(3)
2174(3)
1367(2)
873(3)
327(3)
0
17(1)
17(1)
19(1)
17(1)
17(1)
18(1)
22(1)
15(1)
26(1)
29(1)
23(1)
32(1)
25(1)
23(1)
27(1)
27(1)
33(1)
36(1)
37(1)
39(1)
39(1)
37(1)
52(2)
27(1)
30(1)
33(2)
44(2)
28(1)
34(1)
˚
a ϭ 14.6165(3)
b ϭ 9.7841(2)
c ϭ 19.5286(4)
β ϭ 107.21(10)°
2667.8(8)
a ϭ 6.7896(9)
b ϭ 10.458(1)
c ϭ 11.901(1)
β ϭ 96.668(7)°
839.3(2)
3
˚
Unit cell volume /A
Number of formula units Z
4
2
Calculated density /g·cmϪ3
3.982
3.721
10.904
6.6° < 2θ < 55.0
1614
Absorption coefficient /mmϪ1 11.571
0
0
Range of data collection
Number of independent
reflections
Number of refined parameters 206
Ratio reflections / parameters 15.6
Rint on averaging reflections
Crystal size /mm
Absorption correction
R(ΗFΗ) for Fo > 4σ(Fo)
R(ΗFΗ) for all reflections
Rw(F2)
8.9° < 2θ < 55.0°
3217
1230(3)
1261(4)
0
0
Ϫ1245(3)
1250(4)
1236(4)
0
101
16.0
0.027
0.2 ϫ 0.3 ϫ 0.3
0.023
0.3 ϫ 0.2 ϫ 0.35
semi-empirical [18] semi-empirical [18]
0.028
0.034
0.079
1.26 / Ϫ1.34
0.052
0.083
0.1163
1.89 / Ϫ0.82
0
1251(4)
0
0
1741(6)
0
1250(4)
max. and min. electron
Ϫ3
˚
density /e·A
4447(2)
4481(2)
Ϫ112(5)
291(5)
328(3)
857(3)
wards, the solvent volume was reduced to one third of its original
volume by distillation. Keeping the temperature of the concen-
trated solution constant at 20 °C by a water bath, red crystals of 2
deposited in quantitative yield. Raman spectra of the solid taken
from different regions of the crystalline material showed only the
presence of 2.
N(1)
C(2)
N(2)
0
2251(6)
1844(6)
Table 3. Atomic coordinates (ϫ 104) and equivalent isotropic
2
3
˚
displacement parameters /A ϫ 10 for Te4[AsF6]2 ·C2N2 (2). Ueq is
defined as one third of the trace of the orthogonalized Uij tensor.
Crystal Structure Determinations
Crystals of both compounds are very sensitive towards oxidation,
hydrolysis and the loss of C2N2. So crystals were selected at Ϫ50 °C
under inert oil (Fromblin, Aldrich Inc.) and transferred into the
cold nitrogen stream of the crystal cooling device of a Bruker-Non-
ius Kappa-CCD diffractometer equipped with graphite monochro-
matized Mo-Kα radiation. Data collections were performed in all
cases at Ϫ150 °C (123 K). Both crystal structures were solved by
direct methods and refined based on F2 with anisotropic displace-
ment parameters for all atoms [17]. A semiempirical absorption
correction was applied to all data sets [18]. Table 1 contains the
crystallographic data and details of the structure determinations,
Table 2 and Table 3 the positional parameters of the atoms. Further
crystallographic data like coefficients of the anisotropic tempera-
ture factors have been deposited [19]. Graphical representations
were made using the program DIAMOND [20].
x
y
z
Ueq
Te(1)
Te(2)
As(1)
F(1)
F(2)
F(3)
F(4)
F(5)
F(6)
C(1)
N(1)
962(1)
1321(2)
Ϫ327(2)
168(13)
1626(15)
1337(15)
Ϫ729(14)
Ϫ2191(15)
Ϫ1845(16)
Ϫ4890(20)
4880(20)
1548(1)
Ϫ926(1)
5539(1)
6207(7)
6421(8)
4331(8)
4901(8)
4669(9)
6789(8)
4364(14)
6746(13)
4453(1)
955(1)
30(1)
33(1)
29(1)
38(2)
50(2)
51(2)
50(2)
59(3)
62(3)
45(4)
65(4)
2888(1)
4214(6)
2461(7)
3272(7)
1561(7)
3319(8)
2521(8)
5093(14)
4810(13)
reaction vessel under SO2/C2N2 gas pressure. The FT-Raman spec-
tra were taken from red crystals adherent at the inner wall of a
compartment of the “H-shaped” vessel.
Raman Spectra
FT-Raman spectra on solid samples of 1 and 2 and of liquid C2N2
were recorded with a Bruker FT Raman spectrometer RFS100. The
Results and Discussion
excitation was provided by a Nd:YAG laser of 1064 nm output. Synthesis
The data for both compounds (resolution 4 cmϪ1, 1000 scans, laser
It is well known that AsF5 in liquid SO2 dissolves elemen-
power 25 mW, 20 °C) and for the liquid (resolution 4 cmϪ1, 500
scans, 200 mW, 20 °C) were obtained in the 180° backscattering
geometry. Since both investigated solid compounds are very sensi-
tal tellurium under oxidation to Te64ϩ or Te42ϩ polycationic
clusters, depending on the molar amount of AsF5 used. The
tive against air and moisture, samples were irradiated inside the ionic compounds Te6[AsF6]4 ·2SO2 and Te4[AsF6]2 ·SO2 can
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Donor-Acceptor Complexes of Tellurium Polycationic Clusters with Cyanogen
be isolated from such solutions on distilling off the solvent
[7, 21]. The use of a mixture of C2N2 and SO2 gives the
same polycationic clusters and solvate containing crystals
are obtained, which do not contain SO2 but only C2N2. In
these reactions, as a side product a dark brown amorphous
solid is precipitated, which could not be characterized, but
represents probably the polymer of cyanogen, beside other
unknown cyanogen containing products. The polymeriz-
ation of C2N2 is apparently initiated by the strong Lewis
acidic AsF5. This disadvantageous course of the reactions
can be overcome by the use of stock solutions, which con-
tain the respective tellurium clusters as the [AsF6]Ϫ salts in
liquid SO2 without the presence of excess AsF5. Adding
these solutions to mixtures of SO2/C2N2 gives on slow dis-
tilling off the solvents Te6[AsF6]4 ·1.5C2N2 (1) and
Te4[AsF6]2 ·C2N2 (2) as dark red, hydrolytically unstable
crystals in quantitative yield. Cyanogen turnes out to be a
markedly stronger ligand towards the polycationic clusters
in comparison to SO2, since even in the presence of an ex-
cess, SO2 is completely replaced in all reaction products by
C2N2. According to equations (I) and (II) the C2N2 adducts
are obtained by ligand exchange of SO2 against C2N2.
Te6[AsF6]4 ·2SO2 ϩ 1.5 C2N2 Ǟ Te6[AsF6]4 ·1.5C2N2 ϩ 2 SO2 (I)
Te4[AsF6]2 ·SO2 ϩ C2N2 Ǟ Te4[AsF6]2 ·C2N2 ϩ SO2 (II)
Figure 3. The structure of Te6[AsF6]4 ·1.5C2N2 (1) depicted as the
unit cell (top) in a view slightly inclined to the b-axis. [AsF6]Ϫ
anions are shown as filled octahedra, Te6 cations as filled trigo-
In an atmosphere of C2N2 both compounds are ther-
mally stable at ambient temperature. By collecting repeat-
edly Raman spectra from identical solid samples and com-
paring these, no signs of degradation could be detected and
series of identical spectra were obtained.
4ϩ
nal prisms. Cyanogen molecules are drawn as ball and stick models.
On bottom a section of the structure is shown illustrating the con-
4ϩ
nection of Te6 clusters by the coordinated cyanogen molecules
to a zig-zag chain.
Crystal Structure of Te6[AsF6]4 ·1.5C2N2 (1)
The crystal structure of Te6[AsF6]4 ·1.5C2N2 is made up
4ϩ
of trigonal prismatic Te6 clusters, almost regular octa-
hedral [AsF6]Ϫ anions and cyanogen molecules. Figure 2
shows the molecular entities of the asymmetric unit with
the atomic numbering and Figure 3 the unit cell. The trig-
4ϩ
onal prismatic Te6 cation has crystallographic Cs sym-
metry and is defined by three independent tellurium atoms
forming one triangular face of the cluster. The Te64ϩ polyc-
ation is very close to the ideal D3h symmetry. The bonds
˚
within the triangular faces range from 2.697 to 2.714 A with
˚
an average of 2.706 A. The long bonds along the edges par-
allel to the threefold symmetry axis of the prism range from
˚
˚
3.107 to 3.141 A with an average of 3.129 A. The in-
terplanar angle between the triangular faces is less than 1°.
The mirror plane, which bisects the cluster through the
center of gravity perpendicular to the threefold axis presup-
poses that there is no twist between both triangular faces.
The Te64ϩ cluster in the structure of 1 has the typical struc-
tural features as already observed for the analogous clusters
in Te6[AsF6]4 ·2AsF3 [22], Te6[AsF6]4 ·2SO2 [7, 21],
(Te6)(Se8)[AsF6]6 ·SO2 [23].
Figure 2. The atoms of the asymmetric unit of the structure of
Te6[AsF6]4 ·1.5C2N2 (1). Thermal ellipsoids are drawn at 50 % pro-
bability level; symmetry operations: I: x, Ϫy, z, II: 0.5ϩx, 0.5ϩy,
z, III: 0.5Ϫx, 0.5ϩy, Ϫz, IV: 1.5Ϫx, 0.5Ϫy, Ϫz; selected bond
˚
lengths /A: Te(1)ϪTe(2) 2.6966(4), Te(1)ϪTe(3) 2.7139(4),
Te(2)ϪTe(3) 2.7078(4), Te(1)ϪTe(1)I 3.1067(6), Te(2)ϪTe(2)I
3.1413(6), Te(3)ϪTe(3)I 3.1399(7), Te(3)ϪN(2) 2.886(6),
C(1)ϪN(1) 1.138(12), C(1)ϪC(1)II 1.362(18), C(2)ϪN(2) 1.138(12),
C(2)ϪC(2)IV 1.396(11).
Z. Anorg. Allg. Chem. 2009, 692Ϫ699
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695

J. Beck, M. Zink
ARTICLE
The five symmetrically independent [AsF6]Ϫ anions all general position. The AsF6 octahedron is almost regular,
occupy special positions in the mirror plane for As(1), the FϪAsϪF angles deviate maximally by 1.8° from rec-
As(3), As(5) or in the 2/m center for As(2), As(4) and have tangularity and the AsϪF distances vary between 1.687(9)
˚
therefore Cs and C2h symmetry, respectively. Only slight de- and 1.739(9) A. Comparable bond lengths are found in
viations from ideal octahedral symmetry are found, indi- other compounds with hexafluorido arsenate(V) ions [1].
cated by AsϪF bonds, which span the narrow range be-
˚
tween 1.698 and 1.750 A and FϪAsϪF angles between 86.9
and 93.2°, and 176.4 and 180.0°.
There are two different cyanogen molecules in the struc-
ture of which the non coordinating molecule, defined by the
atoms C(1) and N(1), is centered at the special position
2/m giving the molecule C2h symmetry. The second C2N2
molecule, defined by the atoms C(2) and N(2), is located in
an inversion center giving it Ci symmetry. The CϪC and
CϪN bonds of both molecules are identical within stand-
Figure 4. The atoms of the asymmetric unit of the structure of
Te4[AsF6]2 ·C2N2 (2). Thermal ellipsoids are drawn at 50 % proba-
bility level; symmetry operations: I: Ϫx, Ϫy, 1 Ϫz, II: 1 Ϫx, 1 Ϫy,
˚
ard deviations. The CϵN bond lengths of 1.138 A are
˚
slightly increased in comparison to 1.127 A found for
˚
1 Ϫz; selected bond lengths /A and angles /°: Te(1)ϪTe(2) 2.671(1),
the respective bonds in crystalline cyanogen [24]. The
NϵCϪC angles of 179° [N(1)ϪC(1)ϪC(1)II] and 178°
[N(2)ϪC(2)ϪC(2)III] deviate only slightly from that in crys-
talline cyanogen [179.6(2)°] [24]. Comparable bond lengths
and angles for the coordinated C2N2 molecule were found
in the recently presented [Zn(NCCN)6][AsF6]2 [12].
Te(1)ϪTe(2)I 2.664(1), Te(1)ϪN(1)II 3.369(13), C(1)ϪN(1)
1.166(19), C(1)ϪC(1)II 1.35(3), Te(1)ϪTe(2)ϪTe(1)I 90.18(3),
Te(2)ϪTe(1)ϪTe(2)I 89.82(4), N(1)ϪC(1)ϪC(1)II 174.(2).
A common feature of all structures with square planar
2ϩ
E4 (E ϭ S, Se, Te) cations is the environment around the
˚
Within a sphere of 3 A radius around each tellurium
polycation. Generally, the shortest contacts are found by
atoms located in the plane and over the edges of the E4
square unit. The next short contacts are made up by atoms
which are located along the extension of the diagonals of
the square. In the structure of Te4[AsF6]2 ·C2N2 there is one
fluorine atom bridging each edge of the square planar tetra-
tellurium cation with deviation from the plane of the ring
atom of the Te64ϩ cation nine fluorine atoms and two nitro-
gen atoms are coordinated with the shortest Te···F and
˚
Te···N contacts found at 2.809 and 2.886 A. Expanding the
˚
coordination sphere to a radius of 3.5 A, a total of 40 fluor-
ine atoms but still two nitrogen atoms N(2) are coordinated
to the six tellurium atoms of the cluster. This coordination
4ϩ
pattern of Te6 clusters by the fluorine atoms of fluorido-
˚
of maximally 0.21 A. There are several close charge transfer
contacts between (Te42ϩ)···F and (Te42ϩ)···N, creating the
coordination environment as shown in Figure 5. The short-
est contacts Te···F are found as expected in the plane of the
metallate counterions is comparable with those known in
the literature. As expected, the displacement ellipsoids of
the atoms of the non-coordinating cyanogen are significant
more voluminous than for the coordinating cyanogen. The
2ϩ
Te4 polycation, capping the edges of the square and the
˚
Te(3)···N(2) distances are uniformly 2.886(6) A and the
shortest contacts Te···N are found along the extension of
Te(3)···N(2)ϵC(2) angles of 161.5(5)° deviate considerably
the diagonals of the cation. The cyanogen molecules act
2ϩ
from linearity. The C2N2 molecules act as N,NЈ-bridging
as N,NЈ-bridging ligands, each coordinated to four Te4
4ϩ
ligands between each two trigonal prismatic Te6 cations
clusters, making up a two-dimensional polymeric network
resulting in one-dimensional zigzag shaped chains
ϪTe6ϪNCCNϪTe6ϪNCCNϪ running along the crystallo-
graphic b-axis (Figure 3).
Crystal Structure of Te4[AsF6]2 ·C2N2 (2)
The crystal structure of Te4[AsF6]2 ·C2N2 is made up of
2ϩ
square-planar Te4
cations, almost regular octahedral
[AsF6]Ϫ anions and cyanogen molecules. Figure 4 shows the
molecular entities of the asymmetric unit with the atomic
numbering and Figure 6 the unit cell. The Te4 ion is lo-
2ϩ
cated at an inversion center giving it crystallographic Ci
symmetry and is generated by two independent tellurium
atoms. The TeϪTe bonds lengths within the cluster cation
˚
are 2.671(1) and 2.664(1) A and the TeϪTeϪTe angles are
90.18(3) and 89.82(4)°, which compares well with other
2ϩ
Figure 5. View of the coordination sphere of the Te4 cation the
2ϩ
compounds containing the Te4 cation [1]. The one crys-
structure of Te4[AsF6]2 ·C2N2 (2) with all Te···F and Te···N con-
tallographically independent [AsF6]Ϫ anion is located on a tacts up to 3.5 A.
˚
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Z. Anorg. Allg. Chem. 2009, 692Ϫ699

Donor-Acceptor Complexes of Tellurium Polycationic Clusters with Cyanogen
spread out in the crystallographic a-b-plane (Figure 6). The nounced in the case of the higher charged Te64ϩ in compari-
arrangement of the molecules in this structure can be de- son to Te42ϩ. Accordingly, the respective shortest Te···N
rived from the anti-CaF2 or Li2O type. The [AsF6]Ϫ anions distances in the crystals of 2.886 for 1 and 3.369 A for 2
˚
2ϩ
make up a distorted cubic net, in which the Te4 cations differ strongly. The effect of the increase of the frequency
and the C2N2 molecules occupy alternatingly the cubic- of the stretching vibration ν(CϵN) for coordinated
shaped holes.
nitriles is known and has for example been observed
with SbCl5 ·C2N2 ·SbCl5 [8], {[Ag(NCCN)2][AsF6]}n [9],
[Cd{(CN)2}nSO2][AsF6]2 [10], [Zn(NCCN)6][AsF6]2 [12],
[Ni(NCCN)x][AsF6]2 [12], and other nitrile complexes [25].
Figure 7. Section of the superposed FT-Raman spectra in the
CϵN bond stretching region of Te6[AsF6]4 ·1.5C2N2 (1),
Te4[AsF6]2 ·C2N2 (2), and liquid cyanogen (C2N2).
Figure 6. The structure of of Te4[AsF6]2 ·C2N2 (2). On top the unit
2ϩ
cell is shown. [AsF6]Ϫ anions are depicted as filled octahedra, Te4
cations and cyanogen molecules as ball and stick models. On bot-
tom the two-dimensional net made up by Te42ϩ cations and coordi-
nating cyanogen molecules is shown.
Figure 8. Section of the superposed FT-Raman spectra in the re-
gion between 700 and 90 cmϪ1 of Te6[AsF6]4 ·1.5C2N2 (1),
Te4[AsF6]2 ·C2N2 (2), and liquid cyanogen (C2N2).
Raman Spectroscopy
The Raman spectra of solid Te6[AsF6]4 ·1.5C2N2 (1) and
Te4[AsF6]2 ·C2N2 (2) are characterized by the most intense
Further strong bands occur in the region between 250
4ϩ
bands at 2349 cmϪ1 for 1 and 2331 cmϪ1 for 2, which orig- and 90 cmϪ1 and represent the cluster modes of Te6 and
2ϩ
4ϩ
inate from the stretching vibration ν(CϵN). The existence Te4 (Figure 8). For an isolated trigonal prismatic Te6
of a significant σ donor interaction between the lone pair system with ideal D3h symmetry twelve fundamental vi-
of the CN groups of cyanogen and the Te atoms of the brations are expected which are classified as Γvib ϭ 2AЈ1 ϩ
4ϩ
2ϩ
cationic clusters Te6 and Te4 is indicated by the vi- AЉ1 ϩAЉ2 ϩ 2EЈ ϩ 2EЉ. AЈ1 and EЉ are only Raman active
brational frequencies of the symmetric CϵN stretching modes, whereas AЉ1 is inactive in both Raman and IR, and
mode, since these modes were found to be shifted to higher EЈ is active in both Raman and IR. The bands at 246 and
wave numbers by 22 cmϪ1 for 1 and 4 cmϪ1 for (2) with 130 cmϪ1 are related to the AЈ1 mode. The lower point sym-
respect to uncoordinated liquid cyanogen (Figure 7). The metry (Cs) of the cluster cation in the solid state causes a
symmetrical “end-on” dihapto bonding mode of cyanogen splitting of the band normally located at 179 cmϪ1 into 181
present in the crystal structures is consistent with the and 176 cmϪ1 (assigned as EЈ mode). We suggest this band
Raman spectra. The frequency shift is much more pro- splitting and the large numbers of isotopes of moderately
Z. Anorg. Allg. Chem. 2009, 692Ϫ699
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
697

J. Beck, M. Zink
ARTICLE
high abundance for tellurium causes a bandϪbroadening Table 4. FT-Raman spectra bands of Te6[AsF6]4 ·1.5C2N2 (1),
Te4[AsF6]2 ·C2N2 (2), and liquid cyanogen.
which covers the weak EЉ mode. The remaining bands in
the spectrum of 1 at 119 and 96 cmϪ1 can be assigned to a
1
2
C2N2
Assignment
lattice mode and to the second EЈ mode, respectively. The
2349
889
2331
853
2327
849
νs(CϵN)
ν(CϪC)
bands at 678 and 367 cmϪ1 can be assigned to the stretch-
ing and deformation modes of the [AsF6]Ϫ anions. The 864, 852a)
lower point symmetry of the anion compared to the ideal
ν(CϪC)
Ϫ
678
506
670
506
367
ν(AsF6 )
505
δ(CϪC), [δ(SO2)]
octahedral symmetry causes a splitting of bands which is
367
Ϫ
δ(AsF6
)
seen in the spectrum of 1 by a broadening of bands. The
4ϩ
246
ν(Te62ϩ
)
)
)
)
)
band at 506 cmϪ1 is identified as deformation mode
216
ν(Te42ϩ
ν(Te44ϩ
ν(Te64ϩ
ν(Te6
187c)
δ(NCϪCN) by comparison with the spectrum of liquid cy-
181, 176
129
118
anogen. Weak and moderate resolved bands at 889, 864 and
852 cmϪ1 can be assigned to the ν(CϪC) stretching mode
of coordinated and solvate cyanogen.
lattice mode
2ϩ
106
ν(Te4
)
2ϩ
For an isolated square planar Te4 unit with ideal D4h
94 broadb)
4ϩ
96
ν(Te6
)
symmetry six fundamental vibrations are expected which
are classified as Γvib ϭ A1g ϩ B1g ϩ B2g ϩB2u ϩ Eu. The a) ν(CϪC) stretching mode of solvate cyanogens. b) Intermolecular
translational and rotational interactions. c) B2g mode or lattice
vibration.
molecule has an inversion center and so the mutual ex-
clusion rule is valid. A1g, B1g and B2g are only Raman active
modes, Eu is only IR active, and B2u is inactive. The A1g
mode is identified at 216 cmϪ1 and the band at 187 cmϪ1 is properties of cyanogen in comparison to SO2. The existence
assumed to be the B2g mode or a lattice vibration. The band of a significant σ donor interaction between the nitrile
at 106 cmϪ1 in the low frequencies region can be assigned groups of the cyanogen moieties and the polycationic tel-
to the B1g mode. The bands at 670 and 367 cmϪ1 can be lurium clusters is indicated by the vibrational frequencies
assigned to the symmetrical stretching and deformation of the symmetric CN stretching mode in the Raman spec-
modes of the [AsF6]Ϫ anions. Weak bands at 853 and tra, which were found to be shifted to slightly higher wave
506 cmϪ1 are assigned to the stretching and deformation numbers with respect to uncoordinated cyanogen.
vibrations of ν(CϪC), δ(CϪC) of cyanogen by comparison
with the spectrum of liquid cyanogen.
These results became the starting point for further studies
of Lewis acid-base complexes and coordination polymers
Table 4 summarizes the observed Raman bands of crys- between CN group bearing molecules and tellurium poly-
talline Te6[AsF6]4 ·1.5C2N2 (1), Te4[AsF6]2 ·C2N2 (2), and cationic clusters [29]. We found that neutral polynitriles
of liquid cyanogen together with the tentative assignment with a low lying HOMO are suitable as ligands towards the
which is based on literature data [25Ϫ27]. In liquid C2N2 polycations, whereupon we will report in due course.
the region around 100 cmϪ1 is dominated by a broad inten-
sive band. Our recent low-temperature Raman measure-
Acknowledgement
ments of solid sulfur dioxide and solid cyanogen between
Ϫ35 °C and Ϫ130 °C and a group theoretical analysis
based on the known orthorhombic crystal structure of
C2N2 [28] showed that the lattice vibrations are in the same
region. So we conclude that the broad band in liquid cyano-
gen appreciably originates from intermolecular interactions
in the condensed phase.
We thank J. Daniels for encouraging help with the isolation of crys-
tals at low temperature and for the recording of the diffraction data
sets, and D. Ernsthäuser for the low temperature Raman measure-
ments and the fruitful discussions on the vibrational spectra.
References
[1] S. Brownridge, I. Krossing, J. Passmore, H. D. B. Jenkins, H.
K. Roobottom, Coord. Chem. Rev. 2000, 197, 397.
[2] a) J. D. Corbett, Prog. Inorg. Chem. 1976, 21, 129; b) T. A.
O’Donell, Chem. Soc. Rev. 1987, 16, 1.
[3] a) R. J. Gillespie, J. Chem. Soc., Rev. 1979, 8, 315; b) A. N.
Kuznetsov, B. A. Popovkin, K. Stahl, M. Lindsjö, L. Kloo,
Eur. J. Inorg. Chem. 2005, 4907.
[4] T. A. O’Donell, Superacids and Acidic Melts as Inorganic
Chemical Reaction Media, VCH Publishers, New York, 1993.
[5] J. Beck, Coord. Chem. Rev. 1997, 163, 55.
[6] J. Beck, F. Steden, A. Reich, H. Foelsing, Z. Anorg. Allg. Chem.
2003, 629, 1073.
[7] R. C. Burns, R. J. Gillespie, W. C. Luk, D. R. Slim, Inorg.
Chem. 1979, 18, 3086.
[8] a) T. M. Klapötke, H. Nöth, T. Schütt, M. Suter, M. Warch-
hold, Z. Anorg. Allg. Chem. 2001, 627, 1582; b) I. C. Tornie-
porth-Oetting, T. M. Klapötke, T. S. Cameron, J. Valkonen, P.
Conclusion and Outlook
The reaction of tellurium with arsenic pentafluoride in
liquid SO2 in the presence of cyanogen led to the formation
of the first characterized Lewis acid-base complexes
between
a
polynitrile and
a
polycationic cluster.
Te6[AsF6]4 ·2SO2 and Te4[AsF6]2 ·SO2 are suitable starting
compounds for ligand exchange reactions as a result of the
substitutional lability of the SO2 ligands. In the crystalline
hexafluorido arsenates Te6[AsF6]4 ·1.5C2N2 (1) and
Te4[AsF6]2 ·C2N2 (2) all weak coordinative Te···OϪSϪO
bonds are replaced by stronger Te···NCϪCN bonds, even if
an excess of SO2 is present in the reaction medium. This
distinct reaction behavior underlines the higher nucleophilic
698
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Z. Anorg. Allg. Chem. 2009, 692Ϫ699

Donor-Acceptor Complexes of Tellurium Polycationic Clusters with Cyanogen
Rademacher, K. Kowski, J. Chem. Soc., Dalton Trans. 1992,
537.
[9] H. W. Roesky, H. Hofmann, J. Schimkowiak, P. G. Jones, K.
Meyer-Bäse, G. M. Sheldrick, Angew. Chem. 1985, 97, 403; An-
gew. Chem. Int. Ed. Engl. 1985, 24, 417.
[10] H. W. Roesky, J. Schimkowiak, M. Noltemeyer, G. M. Sheld-
rick, Z. Naturforsch., Teil B 1988, 43, 949.
[11] B. Corian, M. Basato, G. Favero, P. Rosano, Inorg. Chim. Acta
1984, 85, L27ϪL30.
[12] J. Beck, M. Zink, Z. Anorg. Allg. Chem. 2009, 635, 687.
[13] A. B. Elkins, Chemistry of Industrial Toxicology, John Wiley
and Sons, Inc., New York, 1950.
[14] Young, Scientific Glassware, 11 Colville Road, Acton, London,
W3 8BS, England.
of the authors and the literature citation and the deposit
numbers CSD-420262 for Te6[AsF6]4 ·1.5C2N2, CSD-420263
for Te4[AsF6]2 ·C2N2. Details about inquiries are given on
www.fizinformationsdienste.de.
[20] DIAMOND, Crystal Impact Comp., Bonn, Germany, 2005.
[21] J. Beck, F. Steden, Acta Crystallogr., Sect. E 2003, 59, i158.
[22] R. J. Gillespie, W. Luk, D. R. Slim, J. Chem. Soc., Chem. Com-
mun. 1976, 791.
[23] M. J. Collins, R. J. Gillespie, J. F. Sawyer, Acta Crystallogr.,
Sect. C 1988, 44, 405.
[24] A. S. Parkes, R. E. Hughes, Acta Crystallogr. 1963, 16, 734.
[25] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th edn., Wiley, New York, Chiches-
ter, Brisbane, Toronto, Singapore, 1986.
[15] G. Brauer, Handbuch der Präparativen Anorganischen Chemie,
3rd edn., Ferdinand Enke Verlag, Stuttgart, 1975, p. 629.
[16] R. P. Cook, P. L. Robinson, J. Chem. Soc. 1935, 1001.
[17] G. M. Sheldrick, SHELX97 [includes SHELXS97,
SHELXL97, CIFTAB] Ϫ Programs for Crystal Structure
Analysis (Release 97Ϫ2), Universität Göttingen, Germany, [29] Parts of this work were presented at the 30 Reuniao Anual da
1998.
[18] Z. Otwinowski, W. Minor, SCALEPACK, Macromolec. Crys-
tallogr. A 1997, 276, 307.
[19] Detailed crystallographic data can be obtained from the
Fachinformationszentrum Karlsruhe by quoting the names
[26] R. C. Burns, R. Gillespie, Inorg. Chem. 1982, 21, 3877.
[27] J. Weidlein, U. Müller, K. Dehnicke, Schwingungsspektroskopie,
Georg Thieme, Stuttgart, New York, 1982.
[28] B. Andrews, A. Anderson, B. Torrie, J. Raman Spectrosc. 1984,
15, 67.
a
˜
´
´
´
Sociedade Brasileira de Quımica, Aguas de Lindoia Ϫ SP,
Brasil, 2007, and at the Wissenschaftsforum Chemie, Ulm,
Germany, 2007.
Received: December 29, 2008
Published Online: February 27, 2009
Z. Anorg. Allg. Chem. 2009, 692Ϫ699
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
699