Two modifications of copper(I) Octahedro-hexatungsten(II) tetradecabromide, Cu2[W6Br14]

Article abstract of DOI:10.1002/(SICI)1521-3749(199806)624:6<959::AID-ZAAC959>3.0.CO;2-U

The reaction of W₆Br₁₂ with CuBr sealed in an evacuated silica tube at the temperature gradient 925/915 K and annealing at 625/300 K yields a mixture of orthorhombic α-Cu₂[W₆Br₁₄] and cubic β-Cu₂[W₆Br₁₄] in the low temperature zone. α-Cu₂[W₆Br₁₄] crystallizes in the space group Pbca (no. 61), a = 15.126 A, b = 9.887 A, c = 15.954 A, Z = 4, oP88, and β-Cu₂[W₆Br₁₄] crystallizes in the space group Pn3 (no. 201), a = 13.391 A, Z = 4, cP88. The crystal structures are built up by [(W₆Brⁱ₈)Br^a₆] ^2- cluster anions and Cu⁺ cations. The cluster anions show only in the peripheral shells small deviation from m3m symmetry (d(W-W) = 2.630 A; d(W-Brⁱ) = 2.618 A; d(W-Br^a) = 2.614 A). The anions are arranged in a slightly compressed bcc pattern (α) and ccp (β) pattern, respectively. The Cu⁺ cations are trigonal-planar coordinated by Br^a ligands with d(Cu-Br) = 2.377 A (α) and 2.378 A (β). The cubic β-modification is diamagnetic with an unexpected large susceptibility (X_mol = -884×10^-6 cm³ mol^-1) and have a band gap of 2.8 eV. It decomposes under dynamic vacuum in two steps at 795 K und 1040 K.

Full text of DOI:10.1002/(SICI)1521-3749(199806)624:6<959::AID-ZAAC959>3.0.CO;2-U

Z. anorg. allg. Chem. 624 (1998) 959±964
Zeitschrift f uÈ r anorganische
und allgemeine Chemie

Johann Ambrosius Barth 1998
Two Modifications of Copper(I) Octahedro-Hexatungsten(II)
Tetradecabromide, Cu [W Br ]
2
6
14
Yue-Qing Zheng*
Ningbo/P. R. China, Chemistry Department of Ningbo University
Yuri Grin, Karl Peters and Hans Georg von Schnering*
Stuttgart, Max-Planck-Institut f uÈ r Festk oÈ rperforschung
Received December 27th, 1997.
i
a
Ê
Ê
Abstract. The reaction of W Br with CuBr sealed in an
d(W±Br ) = 2.618 A; d(W±Br ) = 2.614 A). The anions are
6
12
evacuated silica tube at the temperature gradient 925/915 K
and annealing at 625/300 K yields a mixture of orthorhombic
α-Cu [W Br ] and cubic b-Cu [W Br ] in the low tempera-
arranged in a slightly compressed bcc pattern (α) and ccp
+
(b) pattern, respectively. The Cu cations are trigonal-planar
a
Ê
coordinated by Br ligands with d(Cu±Br) = 2.377 A (α) and
2
6
14
2
6
14
Ê
ture zone. α-Cu [W Br ] crystallizes in the space group
2.378 A (b). The cubic b-modification is diamagnetic with an
2
6
14
±6
3
±1
Ê
Ê
Ê
Pbca (no. 61), a = 15.126 A, b = 9.887 A, c = 15.954 A, Z = 4,
oP88, and b-Cu [W Br ] crystallizes in the space group Pn3
unexpected large susceptibility (vmol = ±884 × 10 cm mol )
and have a band gap of 2.8 eV. It decomposes under dy-
namic vacuum in two steps at 795 K und 1040 K.
2
6
14
Ê
(
no. 201), a = 13.391 A, Z = 4, cP88. The crystal structures
i
a 2±
+
are built up by [(W
6
Br
8
)Br
6
]
cluster anions and Cu cat-
ions. The cluster anions show only in the peripheral shells
small deviation from m3m symmetry (d(W±W) = 2.630 A;
Keywords: Ternary copper tungsten bromides; Cu
cluster compound; syntheses; crystal structure; properties
2 6
[W Br14];
Ê
Zwei Modifikationen von Kupfer(I)-octahedro-hexawolframat(II)-
tetradecabromid, Cu [W Br ]
2
6
14
Inhalts uÈ bersicht. Bei der Umsetzung von W Br mit CuBr
nen nur in den peripheren Schalen kleine Abweichungen
6
12
i
Ê
von der Symmetrie m3m (d(W±W) = 2,630 A; d(W±Br ) =
in einer evakuierten Quarzampulle im Temperaturgradien-
ten 925/915 K und nachfolgendem Tempern bei 625/300 K
entsteht ein Gemisch von orthorhombischem α-Cu [W Br ]
a
Ê
Ê
2,618 A; d(W±Br ) = 2,614 A). Die Packung der Anionen
entspricht in α einer leicht gestauchten bcc-Struktur und in b
2
6
14
+
und kubischem b-Cu [W Br ] in der kalten Zone. α-
einem ccp-Muster. Die Cu -Kationen sind in beiden Modifi-
2
6
14
a
Cu [W Br ] kristallisiert in der Raumgruppe Pbca (Nr. 61),
kationen trigonal-planar von Br -Liganden koordiniert mit
2
6
14
Ê
Ê
Ê
Ê
Ê
a = 15,126 A, b = 9,887 A, c = 15,954 A, Z = 4, oP88, und
b-Cu [W Br ] in der Raumgruppe Pn3 (Nr. 201),
d(Cu±Br) = 2,377 A (α) und 2,378 A (b). Die kubische b-Mo-
difikation ist diamagnetisch mit einer unerwartet groûen
2
6
14
±6
3
±1
Ê
a = 13,391 A, Z = 4, cP88. Die Kristallstrukturen sind aus
Suszeptibilit aÈ t (vmol = ±884 × 10 cm mol ), besitzt eine
Bandl uÈ cke von 2,8 eV, und zersetzt sich im dynamischen Va-
kuum in zwei Stufen bei 795 K und 1040 K.
i
a 2±
+
den Cluster-Anionen [(W
6
Br
8
)Br
6
]
und Cu -Kationen auf-
gebaut. Die Cluster-Anionen zeigen in beiden Modifikatio-
1
Introduction
*
Correspondence author:
In the group of ternary-octahedro hexatungsten clus-
ter bromides of the alkali metals, we have successfully
prepared Na[W Br ] [1, 2], Na[W Br ] [2, 3] and
Prof. Dr. H. G. von Schnering
Max-Planck-Institut f uÈ r Festk oÈ rperforschung
Heisenbergstraûe 1
6
13
6
14
A [W Br ] with A = K, Rb, Cs [2, 4]. The structure
2
6
14
D-70569 Stuttgart
of Na[W Br ] contains one-dimensional anionic
6
13
1
i
8
a
4
a-a 1±
2/2
+
chains trans- [(W Br )Br Br ]
and Na
ions.
Prof. Dr. Y.-Q. Zheng
∞
6
Chemistry Department of Ningbo University
Ningbo, Zhejiang, P. R. China
Na[W Br ] is isostructural with Hg[Mo Cl ] [5] and
6
14
6
14
a 1±
i
contains isolated monovalent [(W Br )Br ] cluster
6
8
6

9
60
Z. anorg. allg. Chem. 624 (1998)
anions. The compounds A [W Br ] are derivatives of
the intensities were measured on a four-circle diffracto-
meter. The lattice parameters were refined from the 2 val-
ues of 20 carefully centered reflections. Detailed information
about the crystal data and structure determination are sum-
marized in Table 1. The final positional and displacement
parameters are given in Tables 2 and 3. Additional material
can be ordered referring to the no. CSD-408570 (α-
Cu [W Br ]) and CSD-408569 (b-Cu [W Br ]), names of
the authors and citation of the paper at the Fachinforma-
tionszentrum Karlsruhe, Gesellschaft f uÈ r wissenschaftlich-
technische Information mbH, D-76344 Eggenstein-Leopold-
shafen, Germany.
2
6
14
i
a 2±
divalent [(W Br )Br ]
cluster anions, forming a
6
8
6
filled variant of Hg[Mo Cl ] [5]. The comparison
6
14
of the two cubic compounds, Na[W Br ] and
6
14
K [W Br ], do not indicate cationic size effects in the
2
6
14
structure, but much more changes by electronic ef-
fects. This prompted us to try the synthesis of Cu(I)
compounds, which leads to the discovery of two modi-
fications of Cu [W Br ]. During our studies, Ihmaine,
2
6
14
2
6
14
2
6
14
Perrin and Sergent [6] reported about the cubic modi-
fication of Cu [W Br ], which was prepared by heat-
2
6
14
ing a mixture of WBr , CuBr2 and W powder at
5
a-Cu [W Br ]: The structure was solved by direct
methods and final full-matrix least squares refine-
2
6
14
750 °C. In this work, we report our results on the crys-
tal structures of orthorhombic and cubic Cu [W Br ]
2
6
14
ment. It was recognized later that α-Cu [W Br ] is
2
6
14
as well as on magnetic, optical and thermal properties.
isotypic with Cu [Mo I ] [10].
2
6 14
b-Cu [W Br ]: The cubic unit cell and the space
group (Table 1) suggested that this compound may be
2
Syntheses
2
6
14
A mixture of 500 mg (0.252 mmol) W Br [7] and
7
an evacuated silica tube (1inner = 12 mm, L = 100 mm)
and heated at the temperature gradient 925/915 K for
6
12
isostructural with Na[W Br ] [2, 3] or K [W Br ] [2,
6
14
2
6
14
2 mg (0.50 mmol) CuBr (Fluka, p. a.) was sealed in
4
], but the refinement was not successful with the
parameters of these compounds. Nevertheless, the po-
4
weeks with the starting materials in the high tem-
Table 1 Crystal data for orthorhombic α-Cu [W Br ] and
perature zone. Cu [W Br ] was deposited in the low
2
6
14
2
6
14
cubic b-Cu [W Br ] (T = 293 K)
2
6
14
temperature zone. The silica tube was then kept at
25/300 K with the product at 625 K for 2 days to sub-
lime WBr and WBr to the low temperature zone.
6
Phase
α
b
5
6
Formula; mole mass
Cu W Br14;
2
6
2 6
Cu W Br14;
2
348.85 amu
2348.85 amu
greenish yellow
cube
Pure cubic Cu [W Br ] was obtained in high yield
2
6
14
Crystal shape
greenish yellow
bipyramid
(
> 95%) from the outmost end of the tube. It forms a
dark green sintered aggregate. Next to the sintered
clumps, in direction to the low temperature zone,
grew a small amount of greenish yellow bipyramidal
crystals of the orthorhombic phase.
On grinding, the sintered dark green aggregates
turns greenish yellow. Both modifications are stable in
air. It was difficult to gather sufficient amount of the
orthorhombic phase, and, therefore, the investigations
of properties were done with samples of the cubic
phase.
Crystal size (mm)
Space group
0.10 × 0.10 × 0.10
Pbca (no. 61)
Z = 4
0.12 × 0.10 × 0.10
Pn3 (no. 201)
Z = 4
oP88
a = 13.391(1)
Formula units
Pearson code
oP88
Ê
Unit cell (A)
a = 15.126(2), b = 9.887(1),
c = 15.954(2)
2385.9(9), 6.539
Siemens R3m/V four-circle diffractometer,
Mo Kα radiation (k = 0.71073 A);
Ê
3
±3
V (A ); D
x
(g cm
)
2401.3(5), 6.479
Measurement
Calculations
N (parameter)
Ê
Wyckoff scan mode; 2ϑmax = 55°
direct methods, DIFABS, difference Fourier
syntheses; full-matrix least squares refinement,
unit weights; CSD package [8]
100
57.08
35
57.08
±1
l (mm
)
extinction coefficient
N(hkl) (meas./unique) 3950/2747
0.0009(1)
0.00019(1)
3102/934
715
3
Structure determination
N(hkl) ≥ 4r(F
R(F)
o
)
1627
0.073
Suitable single crystals were selected and fixed in sealed ca-
pillaries. The quality was checked by Laue photographs and
0.048
2
Table 2 Positional and displacement parameters (pm ) for the orthorhombic α-Cu
ment factor: exp[±2p (U11h a* + ´ ´ ´ + 2 U23klb*c*)]
2
[W
6
Br14]; (standard deviations); displace-
2
2
2
Atom
Site
x
y
z
U
11
U
22
U
33
U
12
U
13
U
23
Function
W1
W2
W3
Br1
Br2
Br3
Br4
Br5
Br6
Br7
Cu
8 c
8 c
8 c
8 c
8 c
8 c
8 c
8 c
8 c
8 c
8 c
0.9593(1)
0.0633(1)
0.0972(1)
0.8002(3)
0.6194(3)
0.9917(3)
0.4253(3)
0.4081(4)
0.6495(3)
0.2388(3)
0.2831(4)
0.1574(2)
0.1032(2)
±0.0015(2)
0.0555(5)
0.2422(5)
0.0510(6)
0.2383(5)
0.1173(5)
0.2489(6)
0.0007(7)
0.1300(9)
0.4489(1)
0.5762(1)
0.4285(1)
0.4441(3)
0.5458(3)
0.3022(3)
0.4028(3)
0.6225(4)
0.3159(3)
0.3342(3)
0.7084(5)
80(8)
59(8)
75(8)
43(8)
67(8)
74(8)
74(8)
55(7)
56(7)
19(7)
6(7)
23(7)
40(20)
50(20)
±10(20)
±40(20)
±30(2)
±5(6)
±9(6)
4(6)
24(7)
3(7)
W
W
W
Bri
Bri
Br
6
6
±10(8)
±10(20)
10(20)
60(20)
±50(20)
130(20)
±90(20)
±20(20)
60(30)
6
i
120(20)
130(20)
140(20)
140(20)
250(30)
170(20)
110(20)
160(30)
150(20)
110(20)
230(30)
100(20)
130(20)
160(20)
330(30)
410(50)
130(20)
180(20)
60(20)
210(20)
340(30)
170(20)
140(20)
310(40)
±40(20)
±10(20)
±10(20)
10(20)
70(20)
40(20)
40(20)
40(30)
i
Br
a
Br
Br
Br
a
a
40(20)
±20(20)
±10(30)

Yue-Qing Zheng et al., Two Modifications of Cu [W Br ]
961
2
6
14
2
Table 3 Positional and displacement parameters (pm ) for the cubic b-Cu [W Br ]; origin at 3 (choice 2) (standard devia-
2
6
14
2
2
2
tions); displacement factor: exp[±2p (U h a* + ´ ´ ´ + 2 U klb*c*)]
11
23
Atom
Site
x
y
z
U
11
U
22
U
33
U
12
U
13
U
23
Function
W
24 h
8 e
24 h
24 h
8 e
0.13271(6)
0.1393(2)
0.1886(2)
0.3170(2)
0.4339(3)
±0.02570(6)
x
0.0736(2)
±0.0667(2)
x
0.03214(6)
x
±0.1267(2)
0.0809(2)
x
61(4)
164(8)
85(9)
112(10)
285(13)
79(4)
76(4)
±5(3)
±47(8)
±36(8)
6(9)
±19(3)
5(3)
W
6
i
Br1
Br2
Br3
Cu
U
11
U
11
U
12
U
12
Bri
172(10)
245(12)
159(10)
264(12)
33(8)
±66(9)
3(8)
78(10)
U
12
Br
a
Br
U
11
U
11
35(15)
U
12
sitions of W and Br were found to be correct and,
after several cycles, the Cu atoms were located from
difference Fourier syntheses. The final refinement
gave the composition Cu [W Br ].
2
6
14
4
Physical Measurements
4
. 1 The magnetic susceptibility was measured on a pow-
dered sample (202.3 mg) with the use of a SQUID magneto-
meter (Quantum Design Model MPMS 5.5) in the tempera-
ture range 5 ≤ T(K) ≤ 300 with an applied field of 1 Tesla.
4. 2 The diffuse reflectivity was measured with a Perkin-El-
mer Lambda 9 spectrometer in the range of 250±800 nm. The
powdered sample was loaded under inert condition into a
flat quartz container which was then sealed under dynamic
vacuum.
4. 3 Combined thermogravimetric and mass spectrum mea-
surements (TG±MS) were carried out with a thermogravi-
metric analyzer (STA 429, Netzsch Ger aÈ tebau, Selb) coupled
to a mass spectrometer (Fa. Balzers). The powdered sample
±1
(
15.1 mg) was heated with 10 K min under dynamic va-
cuum up to 1273 K.
5
Results and Discussion
5. 1 Thermal stability
As shown in section 2, the two modifications of
Cu [W Br ] are formed under the conditions of
2
6
14
synthesis at separated zones in the reaction tube. The
cubic modification seems to be formed first and will
be transformed into the orthorhombic modification
below 625 K (annealing in temperature gradient 625/
Fig. 1 Cubic Cu [W Br ]: mass loss with temperature un-
der dynamic vacuum (upper) and simultaneously recorded
mass spectrum (below)
2
6
14
300 K to sublime the higher tungsten bromides). This
corresponds to the smaller mole volume of the ortho-
Under dynamic vacuum, the thermal decompsition
of Cu [W Br ] starts at 795 K (Fig. 1) with the com-
3
±1
3
±1
rhombic form (359.2 cm mol vs. 361.5 cm mol ;
Table 1). We have, therefore, designated the orthor-
hombic phase as the low-temperature modification α-
Cu [W Br ]. With these arguments, the higher sym-
2
6
14
plete loss of 2 CuBr (±12.2%). The residue at 1010 K
was confirmed to be W Br by X-ray powder pat-
6
12
terns. In the second step, W Br is decomposed to
2
6
14
6
12
metric cubic b-Cu [W Br ] is the HT-modification
tungsten at about 1040 K. The gas phase analysis
(mass spectra) shows the evaporation of CuBr in the
first step, and the evaporation of tungsten bromides in
2
6
14
which should be metastable at room temperature. The
expected exothermic phase transformation α → b at
higher temperatures was not yet observed directly, but
the sudden evaporation of some CuBr at about 600 K
+
the second step (Fig. 1). The CuBr2 fragment ob-
served at 1150 K has nothing to do with the thermal
decomposition of Cu [W Br ], because the stoichio-
(
Fig. 1) indicates such a small exothermic process.
2
6
14

9
62
Z. anorg. allg. Chem. 624 (1998)
metrical CuBr mass loss is complete at the first step
+
(
795 K). The CuBr2 fragment, therefore, indicates a
reaction of elementary bromine with CuBr or Cu out-
side the Knudsen cell.
5.2 Magnetism and optical reflection
Cubic b-Cu [W Br ] is diamagnetic with v
=
2
6
14
±1
mol
±
6
3
±
884 × 10 cm mol in agreement with the presence
2
±
of divalent [W Br ] cluster anions and monovalent
Cu ions. The diamagnetic susceptibility is unexpected
large. On one hand, the value fits the sum of the dia-
magnetic increments of about ±830 × 10 cm mol
9]. On the other hand, one misses the contribution of
6
14
+
±
6
3
±1
[
van Vleck paramagnetism (TIP) which is usually ob-
served with this type of cluster compounds
6
3
±1
(
400 ≤ v(TIP) ´ 10 ≤ 600 cm mol ), e. g. with the close
related cubic Tl [W Br ] [2]. The unique coordina-
Fig. 2 Spectrum of diffuse reflection of cubic Cu [W Br14]
2 6
2
6
14
2 6 2 6 2 6
Fig. 3 Unit cells of α-Cu [W Br14] (upper) and b-Cu [W Br14] together with the trigonal antiprismatic Cu Br polyhedra
(below)

Yue-Qing Zheng et al., Two Modifications of Cu [W Br ]
963
2
6
14
+
tion of the Cu cations is the main structural differ-
structure of Cu [Mo Cl ] and Cu [Mo Br ] [10].
2
6
14
2
6
14
ence between b-Cu [W Br ] and all the other corre-
Compared with the recently reported cubic
2
6
14
Ê
Cu [W Br ] with a = 13.3866(6) A [6], our unit cell is
2 6 14
sponding cubic cluster compounds. Maybe this detail
is responsible for the suppressed TIP contribution.
The diffuse reflection spectrum (Fig. 2) shows
Ê
slightly larger (a = 13.391(1) A), but no significant dif-
ferences occur in the atomic parameters.
±
1
the onset of the strong absorption at 22600 cm
The two modifications (Fig. 3) differ mainly by the
packing of the cluster anions, which corresponds to a
slightly compressed bcc pattern in α and a fcc pattern
in b. In the α modification, the clusters are centered
at the orthorhombic point configuration F, which is
very close to a tetragonal point configuration I with
which corresponds to the colour of the compound.
The band gap is E = 2.80 eV. The weak irregularity at
g
±
1
1
7400 cm may indicate a d±d transition.
5. 3 Crystal structures
Ê
c/a) = 0.900 (a = (a/√2 + c/√2)/2 = 10.988 A; c = b =
t t t
9.887 A). In the b modification, the clusters are
centered at the cubic point configuration F.
(
Ê
Orthorhombic α-Cu [W Br ] is isostructural with
2
6
14
Cu [Mo I ] [10], while cubic b-Cu [W Br ] has the
2
6 14
2
6
14
i
8
a 2±
6
Fig. 4 The [(W Br )Br ] cluster anions in α-Cu [W Br ] (a) and b-Cu [W Br ] (b) with displacement ellipsoids (90%
6
2
6
14
2
6
14
probability) (Atomic labelling see Table 2 and 3)
Ê
Table 4 Selected interatomic distances (A) and bond angles (°) for α-Cu [W Br ] and b-Cu [W Br ]
2
6
14
2
6
14
α
b
W1±W2
2.624(2)
2.630(3)
2.632(2)
2.633(2)
2.624(2)
2.629(2)
2.610(5)
2.619(5)
2.612(5)
2.632(5)
2.619(6)
2.613(5)
2.616(5)
2.604(5)
2.632(5)
2.608(5)
2.612(5)
2.618(5)
2.622(5)
2.627(5)
W3±Br7
Br1±Br2
±Br3
2.618(5)
3.702(7)
3.677(7)
3.702(7)
3.776(7)
3.735(7)
3.629(7)
3.714(7)
3.718(7)
3.776(7)
3.697(7)
3.659(8)
3.703(7)
3.714(8)
3.678(8)
3.805(6)
3.713(8)
3.665(6)
3.754(8)
60.3(2)
W±W
±W
±Br1
±Br2
±Br2
±Br2
2.629(1) (2 × )
2.633(1) (2 × )
2.636(3)
2.602(3)
2.616(3)
2.618(3)
2.611(2)
3.728(4) (3 × )
3.727(4) (3 × )
3.677(4) (2 × )
3.653(4)
±
±
±
W2
W3
W3
±Br4
±Br5
±Br6
±Br7
W2±W3
W3
W1±Br1
±
±Br3
±
±
±
±
Br2
Br3
Br4
Br5
Br2±Br3
±Br4
Br1±Br2
±Br3
Br2±Br2
±Br3
±Br3
±Br3
Cu±Cu
Cu±Br3
±Br5
±Br6
±Br7
W2±Br1
3.665(4)
3.771(4)
3.066(8)
2.378(5) (3 × )
±
±
±
±
Br2
Br3
Br4
Br6
Br3±Br4
±Br5
±Br6
±Br7
Br4±Br5
±Br6
i
W3±Br1
W±Br ±W
60.3(4)
±Br2
±Br3
±Br4
Br3±Cu±Br3 120.0(2) (3 × )
±Br7
i
W±Br ±W
Cu±Br5
2.339(9)
2.381(9)
2.410(10)
Br5±Cu±Br6 128.2(4)
Br5±Cu±Br7 124.8(4)
Br6±Cu±Br7 106.8(3)
±
±
Br6
Br7

9
64
Z. anorg. allg. Chem. 624 (1998)
2
±
Ê
The divalent [W Br ] cluster anions (Fig. 4) differ
128°). The shortest Cu±Cu distance is 5.044 A. In the
6
14
by small distortion in the corresponding crystal fields,
namely with respect to the symmetry 1 in the ortho-
rhombic phase and 3 in the cubic structure (Table 4).
b modification, however, the Cu atoms are perfectly
triangular coordinated with d(Cu±Br) = 2.378 A. But,
Ê
the two Cu atoms center two opposite triangular faces
of the slightly compressed trigonal antiprism formed
2
±
On average, however, the [W Br ] cluster anions in
6
14
a
both modifications have practically the same shape
Table 5). The mean bond lengths and intracluster dis-
by six Br ligands around the point configuration
1
2
1 1
2 2
(
F(
). This brings the Cu atoms pairwise at a dis-
i
Ê
Ê
Ê
tances are d(W±W) = 2.630 A, d(W±Br ) = 2.618 A,
d(W±Br ) = 2.614 A, d(Br ±Br ) = 3.703 A, d(Br ±Br ) =
3
tance d(Cu±Cu) = 3.066 A. A detailed analysis of this
a
i
i
i
a
Ê
Ê
cubic structure shows [11] that the compression of the
Ê
1 1 1
2 2
.711 A (Table 5). These values are almost identical
trigonal antiprism around F(2
) results from the
with those of other compounds with the cluster anion
cluster rotation around the threefold axis at F(000)
and do not indicate Cu±Cu interactions.
2
±
[
W Br ] [2, 4]. Again, the W atoms are shifted out-
6 14
i
Ê
side the Br cube by 0.008 A. With respect to the inner
Compared with cubic K [W Br ] with the same ar-
8
2
6
14
a
2±
W octahedra, the Br octahedra are rotated from the
rangement of [W Br ] cluster anions but with differ-
6
6
6 14
ecliptic positions by 0.7±1.7° and 1.1° in both modifica-
tions, which is also observed with other compound, and
which is related to the coordination of the cations by
ent arrangement of cations [4], the distribution of the
copper atoms in the present cubic modification is
I
strongly related to the covalence and size of Cu . It is
a
Ê
the Br ligands.
obvious that the Cu±Br distances of 2.825 A and 2.997±
+
a
+
Ê
The trigonal-planar coordination of Cu by Br li-
3.457 A would be too large to accomodate Cu ions in
gands is shown in Fig. 5. The bond lengths in the α
modification (d(Cu±Br) = 2.339±2.410 A) demonstrate
the octahedral and tetrahedral holes if Cu W Br
would adopt the structure of K W Br [4].
2 6 14
2
6
14
Ê
a considerable distortion (bond angles: 107°, 125°,
Acknowledgement. The authors thank the Fonds der Che-
mischen Industrie for generous financial support. We would
like to express our gratitudes to Ms. E. Br uÈ cher for the mag-
netic measurements, Mr. A. Breitschwert for the recording of
the diffuse reflection spectrum and Mr. A. Schmeding for the
efficient TG±MS measurements.
Ê
Table 5 Mean interatomic distances (A) and angles (°) in
i
a 2±
the [(W Br )Br ] cluster anions of orthorhombic (α) and
cubic (b) Cu [W Br ]. D = [d(W±W) ´ 2 ± d(Br ±Br )]
6
8
6
1
i
i
2
6
14
2
α
b
mean values
Local symmetry
d(W±W)
1
3
m3m
References
2.629(4)
2.618(8)
2.615(6)
3.703(14)
3.717(54)
60.2(4)
0.008
2.631(3)
2.618(14)
2.612(2)
3.703(36)
3.704(55)
60.3(4)
0.009
2.630(1)
2.618(0)
2.614(2)
3.703(0)
3.711(9)
60.3
i
d(W±Br )
a
[1] Y. Q. Zheng, Yu. Grin, H. G. von Schnering, Z. Kristal-
logr. 1996, Suppl. 10, 96.
[2] Y. Q. Zheng, Yu. Grin, K. Peters, H. G. von Schnering,
VI. Europ. Conf. Solid State Chem. Z uÈ rich, 1997, Ab-
stract PB53.
d(W±Br )
i
i
d(Br ±Br )
i
a
d(Br ±Br )
i
W±Br ±W
D
0.008
2.378
Cu±Br
2.377(36)
2.378(5)
[3] H. G. von Schnering, Y. Q. Zheng, Y. Grin, Z. Anorg.
Allg. Chem. in preparation.
[4] Y. Q. Zheng, K. Peters, Y. Grin, H. G. von Schnering,
Z. Anorg. Allg. Chem. 1998, 624, 506.
[
[
5] H. G. von Schnering, Z. Anorg. Allg. Chem. 1971, 385, 75.
6] S. Ihmaine, C. Perrin, M. Sergent, Eur. J. Solid State In-
org. Chem. 1997, 34, 169.
[7] H. Sch aÈ fer, R. Siepmann, Z. Anorg. Allg. Chem. 1968,
3
57, 273.
[
8] L. G. Akselrud, Yu. N. Grin, P. Yu. Zavalii, V. K. Pe-
charski, V. S. Fundamenski, Twelfth Eur. Cryst. Meet-
ing, Collected Abstracts, Moscow, 1989, 3, 155.
[9] A. Weiss, H. Witte, Magnetochemie, Verlag Chemie,
1
973, S. 94.
[
10] A. Peppenhorst, H.-L. Keller, Z. Anorg. Allg. Chem.
+
Fig. 5 Coordination of the Cu cations in the orthorhombic
1996, 622, 663.
(
(
a) and cubic (b) modifications with displacement ellipsoids
90% probability)
[11] H. G. von Schnering, Yu. Grin, Y.-Q. Zheng, to be pub-
lished.