Synthesis, crystal and electronic structure of Cd2PCl 2: Influence of cation on characteristic structural features of pnictide halides of Group 12 metals

Article abstract of DOI:10.1023/A:1023938202282

Cadmium phosphide chloride Cd₂PCl₂ was prepared by the ampule synthesis method at 770 K. Crystals were obtained from the gaseous phase by the chemical transport reaction. The crystal structure of Cd ₂PCl₂ is built of the P₂Cd₆ octahedra, which are linked in layers by sharing four equatorial vertices. The layers alternate in a fashion analogous to that observed in the K ₂NiF₄ structural type and are linked in a three-dimensional framework through the halogen atoms. The characteristic features of the crystal and electronic structures of pnictide halides M ₂PCl₂ (M = Cd or Hg) were considered based on X-ray diffraction data and results of quantum-chemical calculations.

Full text of DOI:10.1023/A:1023938202282

570
Russian Chemical Bulletin, International Edition, Vol. 52, No. 3, pp. 570—575, March, 2003
Synthesis, crystal and electronic structure of Cd PCl :
2
2
influence of cation on characteristic structural features
of pnictide halides of Group 12 metals*
ꢀ
A. V. Olenev, O. S. Oleneva, A. V. Shevelkov, and B. A. Popovkin
Department of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (095) 939 4788. Eꢀmail: shev@inorg.chem.msu.ru
Cadmium phosphide chloride Cd PCl was prepared by the ampule synthesis method at
2
2
7
70 K. Crystals were obtained from the gaseous phase by the chemical transport reaction. The
crystal structure of Cd PCl2 is built of the P Cd octahedra, which are linked in layers by
2
2
6
sharing four equatorial vertices. The layers alternate in a fashion analogous to that observed in
the K NiF4 structural type and are linked in a threeꢀdimensional framework through the
2
halogen atoms. The characteristic features of the crystal and electronic structures of pnictide
halides M PCl (М = Cd or Hg) were considered based on Xꢀray diffraction data and results of
2
2
quantumꢀchemical calculations.
Key words: cadmium, mercury, pnictide halides, crystal and electronic structure.
Cadmium and mercury pnictide halides belong to a
Cd—P—Cl system. By contrast, cadmium and mercury
pnictide halides with the 2 : 1 : 2 stoichiometry have been
broad family of ternary and quaternary phases. The main
data on their crystal structures have been surveyed in the
documented in other systems and possess crystal strucꢀ
1
2
14,17—19
review. In all phases, except for the Cd As Cl compound
tures similar to that of Cd PCl .
Hence, we beꢀ
8
7
2
2
having a unique crystal structure, the coordination enviꢀ
ronment about the pnictogen atoms is tetrahedral regardꢀ
less of the presence or absence of the homonuclear
pnictogen—pnictogen bonds. At the same time, the coorꢀ
dination environment about the cadmium and mercury
lieved that the absence of Cd PCl was associated only
2 2
with the conditions of its synthesis. The main aim of the
present study was to synthesize Cd PCl , determine its
2
2
structure, analyze differences between the Cdꢀ and
Hgꢀcontaining phases, and examine the relationship beꢀ
tween the crystal and electronic structures associated with
the possibility of the construction of inorganic supramoꢀ
lecular architectures based on metal—pnictogen frameꢀ
works.
3
3,4
atoms varies from regular octahedral to nearly linear.
In spite of the fact that the stoichiometry of cadmium
pnictide halides is often identical with that of mercury
pnictide halides, these compounds have different crystal
structures due to the difference in the coordination prefꢀ
erence of these metals. In particular, supramolecular enꢀ
sembles based on the metal—pnictogen frameworks, which
are very typical of mercury,5—12 are rarely observed for
cadmium due to the fact that the linear coordination is
atypical of the latter metal. Only two such compounds,
Results and Discussion
The Cd PCl compound was prepared by the standard
2
2
ampule synthesis. We failed to prepare an individual phase
upon annealing of a stoichiometric mixture by varying the
temperature and annealing time. The maximum yield of
the product was attained upon annealing at 770 K for
12 days with intermediate grindings. However, powder
Xꢀray diffraction of the samples thus prepared also reꢀ
vealed the presence of impurities, among which only
Cd P Cl was identified. Based on analysis of the intensiꢀ
3
4
viz., Cd P Cl and Cd P Br , are known.
7
4
6
5
2
4
In the present work, we synthesized cadmium pnictide
halide Cd PCl and studied its crystal and electronic strucꢀ
2
2
ture. The possibility of the existence of this compound
1
3
was predicted as early as 1963. However, this prediction
1
4,15
was not further confirmed.
Three other phases, viz.,
7
4
6
1
6
3,13
3
Cd P Cl, Cd P Cl ,
and Cd P Cl , were proved to
2
3
4
2
3
7 4 6
ties of the reflections in Xꢀray diffraction patterns, we
estimated the total content of impurities at 10—15%. The
use of a larger number of intermediate grindings as well as
quenching of the sample did not increase the yield of the
product.
be the only thermodynamically stable phases in the
*
Dedicated to Academician I. P. Beletskaya on the occasion of
her anniversary.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 548—553, March, 2003.
066ꢀ5285/03/5203ꢀ570 $25.00 © 2003 Plenum Publishing Corporation
1

Synthesis and structure of Cd PCl2
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
571
2
We succeeded in isolating a singleꢀphase sample and
preparing single crystals suitable for Xꢀray diffraction
analysis after the addition of tin to a mixture of the startꢀ
ing reagents. Apparently, crystals were grown from the
gaseous phase according to the chemical transport reacꢀ
tion due to a certain temperature gradient in the ampule
Cd(2)
Cd(1)
Cl(2)
Cl(1)
(
1—3 °C). Presumably, tin chloride that formed in the
course of the process served as the transporting agent.
Earlier, we have demonstrated2 that thermodynamically
unstable phases could be prepared with the use of tin
halides as transporting agents. Yellow crystals synthesized
by the chemical transport reaction were selected mechaniꢀ
cally in an amount necessary for powder Xꢀray diffraction
analysis. The experimental Xꢀray diffraction pattern was
consistent with that calculated from the structural data.
The crystal structure of Cd PCl was studied by singleꢀ
0
2
2
crystal Xꢀray diffraction analysis (Table 1, Fig. 1). The
structure consists of the P Cd octahedra as building
a
2
6
b
blocks, inside each octahedron two closely spaced phosꢀ
phorus atoms being located. The distance between the
phosphorus atoms (2.18 Å) is close to the P—P single
bond length.21 The phosphorus atoms are located on the
threefold pseudoaxis of the octahedron and each atom is
bound to three cadmium atoms belonging to the nearest
face of the octahedron to form a virtually regular tetraꢀ
hedron.
Two independent cadmium atoms have different coꢀ
ordination environments. The coordination polyhedron
about the Cd(1) atom is a strongly distorted tetrahedron
formed by two P atoms and two Cl atoms (Fig. 2, а). The
distortion is characterized by the P—Cd—P angle of 142°.
The Cd(2) atom is surrounded by one P atom and four Cl
c
Fig. 1. Crystal structure of Cd PCl . The layers of the P Cd
4
octahedra and the chlorine atoms binding these layers are shown.
2
2
2
atoms and its coordination can be described as intermeꢀ
diate between tetragonalꢀpyramidal and trigonalꢀbiꢀ
pyramidal (Fig. 2, b). The P—Cd(2)—Cl(2) angle is
1
57.4°, the Cd(2)—Cl(2) distance is very short (2.48 Å),
Cl(1)
a
Cl(2)
Table 1. Crystallographic parameters and main details of the
refinement of the crystal structure of Cd PCl2
2
Cd(1)
42.0°
Parameter
Characteristic
P
P
1
Formula
Cd PCl2
2
Molecular weight
326.67
Crystal system
Space group
a/Å
b/Å
c/Å
Monoclinic
Cl(1)
P2 /n
b
1
7.736(1)
8.957(1)
7.880(1)
118.92(1)
477.93(1)
4
1
57.4°
Cl(2)
β/deg
V/Å3
Z
dcalc/g cm
µ/mm
Scan range
P
–
3
4.540
10.149
3.04 < θ < 34.39
2105
Cd(2)
–
1
Number of measured reflections
Number of reflections with I ≥ 2σ(I )
Number of refinable parameters
Cl(1)
1956
47
Cl(1)
R (I ≥ 2σ(I ))
0.0455
0.1334
1
Fig. 2. Coordination about the cadmium atoms in the structure
wR (for all reflections)
2
of Cd PCl (ellipsoids are drawn at the 50% probability level).
2
2

572
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Olenev et al.
long to the same structural type. However, the difference
in the relative size of the halogen and pnictogen atoms is
responsible for the fact that the former compound is charꢀ
acterized by a stronger distortion of the coordination polyꢀ
hedra about cadmium, whereas the crystal structure of the
latter loses a center of symmetry. The crystal structure of
Cd PCl differs much from the structures of mercury anaꢀ
a
2
2
1
8
logs, Hg PCl
and the nonꢀisostructural Hg AsCl comꢀ
2
9
2
2 2
1
pound (see Table 2). Although the general motif is reꢀ
tained, the difference between the structures of the cadꢀ
miumꢀ and mercuryꢀcontaining phases is that both the
octahedra within each layer and the layers themselves in
Hg PCl are arranged "properly" in a manner similar to
b
2
2
the K NiF structural type (due to the fact that the
2
4
P—Hg—P angle is 180°), whereas the analogous layers in
Cd PCl are rotated with respect to each other (see Fig. 3).
2
2
In addition, the mercury atoms in Hg PCl are characterꢀ
2
2
ized by the transꢀ2+4 coordination in which two short
bonds are formed with phosphorus atoms (Hg(1) atom)
or phosphorus and chlorine atoms (Hg(2) atom).
The difference between mercuryꢀ and cadmiumꢀconꢀ
taining pnictide halides with the 2 : 1 : 2 stoichiometry
can be attributed to different coordination requirements
Fig. 3. Top views of the layers of the P Cd octahedra in the
2
4
crystal structure of Cd PCl (a) and layers of the P Hg octaꢀ
2
2
2
4
II
II
hedra in Hg PCl (b).
of Cd and Hg . The divalent mercury atoms are inꢀ
volved in two short collinear bonds, thus providing the
formation of K NiF ꢀlike layers, whereas cadmium tends
2
2
2
4
and all other distances between the Cd and Cl atoms are
substantially longer and are in the range of 2.64—2.98 Å
typical of the cadmium—chlorine covalent bond (2.66 Å
in CdCl2,22 2.62—2.86 in Cd P Cl ).
primarily to have a tetrahedral coordination, which leads
to a distortion of these layers. As a consequence, the role
of the halogen atoms changes. Thus, the Cl(1) atom in
Cd PCl is surrounded by the tetrahedral Cd atoms,
3
4
2
3
2
2
The P Cd octahedra share the equatorial vertices ocꢀ
whereas the Cl(2) atom serves as an angular bridge beꢀ
tween the axial Cd atom of one layer of octahedra and the
equatorial Cd atom of the adjacent layer. In Hg PCl ,
2
6
cupied by the Cd(1) atoms to form layers of the general
formula P Cd (Fig. 3). The layers are linked to each
2
4
2
2
other through the chlorine atoms. The mode of alternaꢀ
tion of the layers composed of the octahedra is typical of
oneꢀhalf of the halogen atoms are terminal.
Calculations of the band structures of Cd PCl and
2
2
2
2
the K NiF structural type. Two other cadmium pnictide
Hg PCl in the framework of the extended Hückel theory
2
4
2
2
23
1
4
17
halides, viz., Cd AsCl2 and Cd SbBr , (Table 2) beꢀ
(EHT) demonstrated that the individual features of the
2
2
2
Table 2. Crystallographic data for cadmium and mercury pnictide halides with the 2 : 1 : 2 stoichiometry
Compound
Space group
Unit cell parameters
Reference
a/Å
b/Å
c/Å
α
β
γ
deg
Cd PCl2
P2 /n
7.736
8.957
7.880
—
118.92
—
Present
study
14
17
18
19
19
15
2
1
Cd AsCl2
P2 /с
7.858
8.244
7.643
13.914
11.255
8.899
9.193
9.920
7.977
8.210
11.348
9.911
8.189
8.492
8.539
8.896
12.295
13.995
—
—
—
—
105.73
—
119.95
116.80
115.23
97.61
105.72
92.92
—
—
—
—
109.15
—
2
1
Cd SbBr2
P21
I2/m
2
Hg PCl2
2
Hg AsCl2
C2/m
2
–
Hg As Br *
P1
19
10 18
Hg SbBr **
P2 /с (?)
2
2
1
*
Phase differs in the stoichiometry, but has a similar structure formed as a result of the ordered removal of 1/20 of the
Hg atoms and 1/10 of the Br atoms. ** Crystal structure is unknown.

Synthesis and structure of Cd PCl2
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
573
2
crystal structures of cadmium and mercury phoshpide
chlorides associated with the difference in the coordinaꢀ
tion of the metal atoms are manifested in substantial difꢀ
ferences in their band structures (Figs. 4 and 5). Analysis
of the density of states (DOS) curves demonstrated that
there is the separation in energy between the valence band
and conduction band in the band structure of Cd PCl ,
the top of the valence band being composed predomiꢀ
nantly from the p orbitals of the phosphorus atoms and
the s and p orbitals of the cadmium atom. The Hg PCl
2
2
COOP
a
EF
2
2
1
0
COOP
–
20
–10
0
E/eV
–
1
1
1
0
.5
.0
.5
0
a
–2
EF
–3
–4
–
20
–10
0
E/eV
COOP
.4
–
0.5
0
0
0
0
b
COOP
.4
.3
.2
.1
0
EF
0
0
b
EF
.2
0
–
20
–10
0
E/eV
–
20
–10
0
E/eV
–
–
0.2
0.4
DOS
DOS
c
c
40
3
2
1
0
EF
0
0
2
0
EF
–
20
–10
0
E/eV
–
20
–10
0
E/eV
DOS
0
DOS
0
d
d
3
2
1
4
EF
0
0
EF
20
–
20
–10
0
E/eV
–20
–10
0
E/eV
Fig. 4. Band structure of Cd PCl : a, COOP of the Cd—P bond;
Fig. 5. Band structure of Hg PCl : a, COOP of the Hg—P bond;
2
2
2
2
b, COOP of the P—P bond; c, total DOS and the contribution of
the orbitals of the P atoms; d, total DOS and the contribution of
the s and p orbitals of the Cd atoms.
b, COOP of the P—P bond; c, total DOS and the contribution of
the orbitals of the P atoms; d, total DOS and the contribution of
the s and p orbitals of the Hg atom.

574
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
Olenev et al.
compound has a different band structure in which a rather
narrow band formed almost completely from the mercury
p orbitals is located between the valence and conduction
bands. As can be seen from the crystal orbital overlap
population (COOP) curves, these orbitals are virtually
nonbonding. A more detailed analysis of orbital interacꢀ
tions showed that the d orbitals of mercury make a subꢀ
stantial contribution to the Hg—P bonding interaction at
the top of the valence band. This leads to a stronger and
cation of the product by sublimation. All operations with
moistureꢀsensitive cadmium chloride were carried out in a
dry box.
The preparation was carried out by the standard ampule
synthesis. Equimolar amounts of cadmium, phosphorus, and
cadmium chloride (total weight was 1 g) were placed in a quartz
ampule. The ampule was sealed in vacuo and placed in a furꢀ
nace. Annealing was carried out at 770 K for 6 days and then the
mixture was annealed once again under the same conditions
after intermediate grinding.
Single crystals of Cd2PCl2 were prepared from a mixture of
cadmium chloride, phosphorus, tin, and cadmium in a molar
ratio of 3 : 4 : 1 : 3. Annealing was carried out at 820 K for 2 days
and then the temperature was lowered to 775 K during 6 h. The
reaction mixture was kept at this temperature for 4 days and
then furnaceꢀcooled.
Powder Xꢀray diffraction analysis was carried out on a
STADIꢀP (STOE) powder diffractometer (CuꢀKα1 radiation).
The phase analysis was performed with the use of the automated
PDFꢀ1 database.
1
8
shorter Hg—P bond compared to the Cd—P bond (2.40
and 2.46—2.49 Å, respectively).
In both structures, the P—P distances have equal valꢀ
ues. The corresponding Mulliken populations determined
from the analysis of the band structures also have equal
values. By contrast, the Mulliken populations of the
metal—chlorine bonds are substantially different (0.11 and
0
.06 for cadmium and mercury, respectively). After subꢀ
traction of the contribution of the short Cd(2)—Cl(2)
bond, the corresponding Mulliken population remains
virtually unchanged, whereas the subtraction of the conꢀ
tribution of the short Hg—Cl bond leads to a decrease in
the population to 0.04. In spite of the fact that the absoꢀ
lute values of the Mulliken populations do not provide
complete information on the bond strength, a compariꢀ
son of the values of like compounds enables one to reveal
the tendency for a change in the strength of covalent
interactions. The results of our study demonstrated that
the metal—chlorine bond in Hg PCl is weaker than that
A suitable single crystal of Cd2PCl2 was mounted on a goꢀ
niometric head of an automated Nonius CADꢀ4 diffractometer
(
graphite monochromator, λ(MoꢀKα) = 0.71073 Å, ∼ 20 °C,
ωꢀ2θ scanning technique). The crystallographic parameters and
main details of the refinement of the crystal structure of Cd PCl
2
2
are given in Table 1. The absorption correction was applied
using the standard DIFABS program.
Analysis of the observed systematic absences indicated the
only possible space group P2 /n (No. 14, nonꢀstandard setting).
1
The crystal structure of Cd PCl was solved by direct methods,
2
2
which made it possible to locate the positions of the cadmium
atoms. The remaining atoms were revealed from a series of subꢀ
sequent difference Fourier syntheses alternated with cycles of
the leastꢀsquares refinement. Since the experimental data were
collected to θ = 35°, it was unambiguously determined that the
metal positions were occupied only by cadmium atoms, whereas
tin atoms with a similar scattering power are not involved in the
structure. (The cadmium and tin atoms have 48 and 50 elecꢀ
trons, respectively, and, hence, posses close scattering properꢀ
ties. The difference in the scattering power increases as the
θ angle increases. The Xꢀray data collected to large θ angles
from a highꢀquality crystal makes it possible to distinguish these
atoms.) The final anisotropic refinement was carried out
2
2
in Cd PCl , and more remote chlorine atoms in the former
2
2
structure make only a slight contribution to this bond.
Therefore, the difference in the coordination about
the mercury and cadmium atoms is responsible for subꢀ
stantial differences in the band structures of the correꢀ
sponding phosphide chlorides. The tendency of mercury
to have a linear coordination atypical of cadmium is maniꢀ
fested, on the one hand, in the formation of "proper"
layers of octahedra typical of the K NiF structural type
2
4
and, on the other hand, in the occurrence of a narrow
unoccupied band formed by the p orbitals, which are
not involved in covalent bonding, between the Fermi
level and the conduction band. The presence of such
a band in mercuryꢀcontaining compounds is, apparꢀ
ently, the necessary condition for the formation of
weak guest—host interactions in supramolecular enꢀ
sembles.7
2
against F . The principal interatomic distances and bond angles
are given in Table 3. All calculations were carried out using the
24,25
SHELX97 program package.
*
Calculations of the band structures were carried out in the
tightꢀbinding approximation using the MO LCAO method within
the limits of the extended Hückel theory. The Slaterꢀtype atomic
orbital parameters, viz., ionization potentials and atomic orbital
,11,12
2
6
exponent, were taken from the literature. The geometric paꢀ
rameters of Cd PCl and Hg PCl were taken from the Xꢀray
2
2
2
2
Experimental
diffraction study and literature, respectively.18 The calculations
2
7
were carried out using the BICONꢀCEDiT program package.
Highꢀpurity cadmium (>99.99%) and red phosphorus (97%)
were used as the starting compounds. Phosphorus was purified
by washing with a 30% KOH aqueous solution, water, ethanol
* More detailed data on the study of the crystal structure can be
obtained from Fachinformationszentrum Karlsruhe, Dꢀ76344
EggensteinꢀLeopoldshafen, Germany (fax: +(49) 7247ꢀ808ꢀ666;
eꢀmail: crysdata@fizꢀkarlsruhe.de) on quoting the depository
number CSD 412647.
(
two times), and ether followed by vacuum drying. Anhydrous
cadmium chloride was synthesized by heating cadmium metal
under a stream of dried HCl at 670 K followed by the purifiꢀ

Synthesis and structure of Cd PCl2
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 3, March, 2003
575
2
Table 3. Principal bond lengths (d) and bond angles (ω) in the
9. A. V. Olenev, A. V. Shevel´kov, and B. A. Popovkin,
Zh. Neorg. Khim., 1999, 44, 1957 [Russ. J. Inorg. Chem.,
structure of Cd PCl2
2
1
999, 44, 1853 (Engl. Transl.)].
1
1
0. J. Beck and U. Neisel, Z. Anorg. Allg. Chem., 2000, 626, 1620.
1. J. Beck and U. Neisel, Z. Anorg. Allg. Chem., 2001, 627,
2016.
Bond
d/Å
Angle
ω/deg
Cd(1)—P
Cd(1)—P
2.488(1)
2.493(1)
2.703(1)
2.799(1)
2.461(1)
2.477(1)
2.636(1)
2.841(1)
2.979(1)
2.183(2)
P—Cd(1)—P
P—Cd(2)—Cl(2)
P—P—Cd(2)
P—P—Cd(1)
P—P—Cd(1)
Cd(2)—P—Cd(1)
Cd(2)—P—Cd(1)
Cd(1)—P—Cd(1)
142.00(5)
157.36(5)
108.76(8)
111.12(8)
111.80(7)
108.07(5)
107.82(5)
109.13(5)
12. A. V. Olenev and A. V. Shevelkov, J. Solid State Chem.,
2001, 160, 88.
13. L. Suchow and N. R. Stemple, J. Electrochem. Soc., 1963,
110, 766.
14. A. Rebbah, J. Yazbeck, A. Leclaire, and A. Deschanvres,
Acta Crystallogr., 1980, B36, 771.
15. H. Puff and H. Gotta, Z. Anorg. Allg. Chem., 1966, B343, 225.
16. P. C. Donohue, J. Solid State Chem., 1972, 5, 71.
17. L. N. Reshetova, A. V. Shevel´kov, and B. A. Popovkin,
Koord. Khim., 1999, 25, 875 [Russ. J. Coord. Chem., 1999,
Cd(1)—Cl(2)
Cd(1)—Cl(1)
Cd(2)—P
Cd(2)—Cl(2)
Cd(2)—Cl(1)
Cd(2)—Cl(1)
Cd(2)—Cl(1)
P—P
2
5, 819 (Engl. Transl)].
1
1
8. A. V. Olenev, A. V. Shevelkov, and B. A. Popovkin, J. Solid
State Chem., 1998, 142, 14.
9. A. V. Shevel´kov, E. V. Dikarev, and B. A. Popovkin,
Zh. Neorg. Khim., 1995, 40, 1496 [Russ. J. Inorg. Chem.,
This study was financially supported by the Russian
Foundation for Basic Research (Project No. 00ꢀ03ꢀ
3
2539a).
1
995, 40 (Engl. Transl.)].
References
. A. V. Shevelkov and M. M. Shatruk, Izv. Akad. Nauk, Ser.
Khim., 2001, 321 [Russ. Chem. Bull., Int. Ed., 2001, 50, 337].
. A. V. Shevelkov, E. V. Dikarev, and B. A. Popovkin, J. Solid
State Chem., 1997, 134, 282.
. A. V. Shevelkov, L. N. Reshetova, and B. A. Popovkin,
J. Solid State Chem., 1998, 137, 138.
. M. M. Shatruk, L. N. Reshetova, A. V. Shevel´kov, and
B. A. Popovkin, Zh. Neorg. Khim., 2000, 45, 565 [Russ.
J. Inorg. Chem., 2000, 45, 495 (Engl. Transl.)].
20. M. M. Shatruk, K. A. Kovnir, A. V. Shevelkov, and B. A.
Popovkin, Angew. Chem., Int. Ed., 2000, 39, 2508.
2
2
2
2
1. H. G. von Schnering and W. Hönle, Chem. Rev., 1988,
8, 243.
1
8
2. A. F. Wells, Structural Inorganic Chemistry, Clarendon Press,
Oxford, 1986.
2
3
4
3. J. H. Ammeter, H. B. Bürgi, J. C. Thibeaut, and
R. Hoffmann, J. Am. Chem. Soc., 1978, 100, 3686.
4. G. M. Sheldrik, SHELXSꢀ97, Program for Crystal Strucꢀ
ture Solution, University of Göttingen, Göttingen (Gerꢀ
many), 1997.
5. G. M. Sheldrik, SHELXLꢀ97, Program for Crystal Structure
Refinement, University of Göttingen, Göttingen (Gerꢀ
many), 1997.
2
5
6
7
8
. A. V. Olenev, A. I. Baranov, A. V. Shevel´kov, and B. A.
Popovkin, Eur. J. Inorg. Chem., 2000, 265.
. A. V. Olenev and A. V. Shevelkov, Angew. Chem., Int. Ed.,
2
2
6. P. Pyykkö and L. L. Lohr, Jr., Inorg. Chem., 1981, 20, 1950.
7. M. Brändle, R. Rytz, and G. Calzaferri, BICONꢀCEDiT.
Manual, University of Bern, Bern (Switzerland), 1997.
2
001, 40, 2353.
. A. V. Olenev, A. I. Baranov, A. V. Shevelkov, and B. A.
Popovkin, Eur. J. Inorg. Chem., 2002, 2, 547.
. A. V. Olenev, A. V. Shevel´kov, and B. A. Popovkin,
Zh. Neorg. Khim., 1999, 44, 1911 [Russ. J. Inorg. Chem.,
Received September 27, 2002;
in revised form January 14, 2003
1
999, 44, 1814 (Engl. Transl.)].