[Cd3Cu]CuP10, [Cd3Cu] cluster stabilized in an adamantane-like polyphosphide substructure

Article abstract of DOI:10.1002/zaac.200801414

[Cd₃Cu]CuP₁₀ is the first representative of the adamantane-like polyphosphides featuring a metalloid, tetrahedral [M ₃X] heterocluster, containing only d¹⁰ ions. It was prepared by the mineralization concept for

Full text of DOI:10.1002/zaac.200801414

ARTICLE
DOI: 10.1002/zaac.200801414
[Cd3Cu]CuP10, [Cd3Cu] Cluster Stabilized in an Adamantane-Like
Polyphosphide Substructure
Melanie Bawohl[a] and Tom Nilges*[a]
Dedicated to Professor Reinhard Nesper on the Occasion of His 60th Birthday
Keywords: Copper; Cadmium; Polyphosphides; Metalloid heteroclusters
Abstract. [Cd3Cu]CuP10 is the first representative of the ada-
measurements substantiated the refined composition within the
standard deviation of the experiment. A slow decomposition of
mantane-like polyphosphides featuring a metalloid, tetrahedral
[M3X] heterocluster, containing only d10 ions. It was prepared by [Cd3Cu]CuP10 was proven by DSC measurements and annealing
the mineralization concept for polyphosphides using CuI as the
mineralizer species. The title compound crystallizes cubic in the
experiments. The DSC spectra of different samples showed a broad
exothermic effect starting at 573 K, which could be identified as a
decomposition to new phases. Preliminary results of a single crystal
˚
¯
space group F43m (No. 216), with a ϭ 10.479(2) A and V ϭ
3
˚
1150.9(4) A . It is isostructural to the tin containing coinage-metal structure determination of the main phase after decomposition
polyphosphides [M3Sn]CuP10 with M ϭ Cu, Ag, Au. A perfect
orientation disorder of the [Cd3Cu] heterocluster relative to the
space diagonals of the cubic cell is present, which is characteristic
for the metalloid substructure of this class of compounds. EDX
pointed towards realized structure units closely related to the title
compound, the Cu2P20 and the [Ag3Sn]P7 structure type. A detailed
examination of the structural features of this new compound is still
in progress.
carbon-free inorganic chemistry. Pure tetrahedral tran-
sition-metal cluster like [Ag3Hg]3ϩ and [Ag2Hg2]4ϩ are
known from the mineral tillmansite and closely related
compounds [11]. The structure motive of a homoatomic
[Cd4] cluster is known from the intermetallic compounds
RE4TCd (RE ϭ Y, L a ϪNd, Sm, GdϪTm, Lu; T ϭ Ni, Pd,
Ir, Pt and RE ϭ Y, L a ϪNd, Sm, and GdϪTm, Lu; T ϭ
Co, Ru and Rh) [12aϪb], RE4CoCd (RE ϭ Tb, Dy, Ho)
[12c] and RE23T7Cd4 [12d]. Cd and mixed Cu/Cd cluster
are of various sizes and shapes and are approximants for
the structure of Cd3Cu4 and i-CdCu [12eϪf].
Introduction
Polyphosphides containing an adamantane-like poly-
anion substructure are known for several years now. Begin-
ning with the discovery of [Cu3Sn]CuP10 by Goryunova in
1970 [1] and the structure determination later on [2], a re-
cent progress and improvement in the number of new com-
pounds and their chemical understanding was made. By the
application of the mineralization concept for polytellurides
[3aϪc] and polyphosphides [3dϪe], capable to prepare
compounds featuring 0-dimensional to 2-dimensional poly-
anionic substructures [4], the synthesis and characterization
of [Ag3Sn]CuP10 [5] and [Au3Sn]CuP10 [6] were reported
recently. Within the plethora of phosphides and polyphos-
phides [7] the class of [P10]-adamantane containing com-
pounds show some interesting electronic properties, e.g. the
metalloid character [8, 9] and the pronounced disorder of
the [M3Sn] groups. Closely related to the [P10]-polyphos-
phides are the [M3Sn]P7 polyphosphides (M ϭ Ag, Au) [10],
which contain a polymeric anion substructure and compar-
able metalloid clusters.
Herein we report on the synthesis and characterization
of [Cd3Cu]CuP10, the first compound of an adamantane-
type polyphosphide containing
heterocluster.
a
d10-transition-metal
Experimental Section
Synthesis: Cu3P was prepared from the elements in ideal ratios,
prior to use, in evacuated silica ampoules at 823 K. A total amount
of 1 g of [Cd3Cu]CuP10 was prepared from a 2/3 : 3 : 91/3 mixture of
Cu3P, cadmium (Chempur, 99.999 %) and phosphorous (Chempur,
99.999ϩ%) in evacuated silica ampoules. The starting materials
were heated within 8 h to 1023 K, kept at that temperature for
19 days, and then cooled down to room temperature within 6 h.
Reports on tetrahedral building units formed exclusively
by late transition metals (d10 ions) are rare in the field of
* PD Dr. T. Nilges
A second sample (in the following called as cadmium-rich
E-Mail: nilges@uni-muenster.de
[a] Institut für Anorganische und Analytische Chemie
Westfälische Wilhelms-Universität
Corrensstraße 30
sample), containing starting materials with the ratio Cu3P/Cd/P ϭ
2/3 : 4 : 91/3 was held at a temperature of 923 K for 14 days before
quenching on air. This sample, prepared to identify the de-
composition products of [Cd3Cu]CuP10 at elevated temperatures
48149 Münster, Germany
Z. Anorg. Allg. Chem. 2009, 635, 667Ϫ673
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667

M. Bawohl, T. Nilges
ARTICLE
(see later on) resulted in a mixture of two phases. The purity of
the starting material and the final products was checked by X-ray
powder diffraction and EDX analyses.
plate technology was applied for detection purposes and the read-
out was done using a Fuji BAS-1800 reader. Finely ground samples
were examined using Guinier cameras, operated with Cu-Kα1 radi-
˚
ation (λ ϭ 1.54051 A, germanium monochromator), and Ͱ-quartz
EDX Measurements: Semi-quantitative analyses were performed
with a Leica 420i scanning electron microscope (Zeiss), fitted with
an energy dispersive detector unit (Oxford). Cadmium, copper, and
GaP (P) were used as standards for calibration. A voltage of 20 kV
was applied to the samples. Details concerning the composition of
[Cd3Cu]CuP10 are summarized in Table 1.
was used as an internal standard. All samples were measured at
293 K in transmission geometry.
Table 1. Results from EDX analyses of [Cd3Cu]CuP10, prepared by
the mineralization concept using small amounts of CuI. The pre-
sence of iodine could not be detected in any measurement.
Sample
Composition (calcd./at-%) Composition (EDX/at-%)
Cd/Cu/P
Cd/Cu/P
[Cd3Cu]CuP10 20.0 : 13.3 : 66.7
(Crystal 1)
20(2) : 12(2) : 68(2)
Figure 1. Measured and calculated X-ray powder diffractograms of
[Cd3Cu]CuP10
(Crystal 2)
21(2) : 14(2) : 65(2)
[Cd3Cu]CuP10. The calculated intensities are drawn downwards for
¯
clarity. Space group F43m. Lattice parameters derived from powder
3
˚
˚
data are a ϭ 10.479(2) A, V ϭ 1150.9(5) A at 293 K.
The results are averaged from 5 to 8 independent measurements for
each sample. Standard deviations are estimated from the variations
of the measurements. According to Table 1, the averaged value for
all analyses results in a composition of Cd3.0(1)Cu1.9(3)P10.0(5), in
good accordance with the refined composition derived from single
crystal structure determinations.
A rather complex diffractogram was found analysing the cadmium-
rich sample prepared at 923 K (see Synthesis section). We could
identify at least three different phases of which the minor compo-
nent was the title compound [Cd3Cu]CuP10.
X-ray Single Crystal Diffraction: Intensity data of two different
EDX analyses of selected crystals separated from the bulk residue
of the cadmium-rich sample resulted in an averaged composition
of Cd/Cu/P ϭ 15 : 2 : 33. Obviously this phase is enriched in Cd
compared with the title compound.
crystals were collected at 293 K and at 150 K on a STOE IPDS-II
˚
image plate system operated with Mo-Kα radiation (λ ϭ 0.71073 A)
in oscillation mode. Temperature-dependent measurements were
done using a Cryostream plus system (Oxford). The temperature
X-ray Powder Diffraction: Phase analysis of [Cd3Cu]CuP10 (Figure was calibrated by measuring the two reversible phase transitions of
1) was performed by X-ray powder diffraction at 293 K. Image Ag5Te2Cl at 244 and 334 K as given in the literature [13]. A tem-
Table 2. Crystallographic data for [Cd3Cu]CuP10, collected from two different crystals at 293 and 150 K (crystal 2 only).
Crystal 1
(293 K)
Crystal 2
Crystal 2
(150 K)
(293 K)
Empirical formula
refined composition
Molar mass /g·molϪ1
[Cd3Cu]CuP10
Cd2.8(1)Cu2.2(1)P10
762.3
Cd2.8(1)Cu2.2(1)P10
763.3
Cd3.2(1)Cu1.8(1)P10
782.6
10.461(1)
1144.8(4)
4
4.539
0.10 ϫ 0.07 ϫ 0.05
˚
Unit cell dimension a /A
10.479(2)a)
1150.9(5)
4
10.479(2)a)
1150.9(5)
4
3
˚
Unit cell volume /A
Z
Calculated density /g·cmϪ3
Crystal size /mm
Space group
4.404
0.09 ϫ 0.07 ϫ 0.05
4.398
0.10 ϫ 0.07 ϫ 0.05
¯
F43m
2θ range
hkl range
6.74Ϫ60.24
Ϫ14 to 14
Ϫ14 to 14
Ϫ14 to 14
3124, 0.0305
15
6.74Ϫ60.0
Ϫ14 to 14
Ϫ14 to 14
Ϫ14 to 14
3096, 0.0185
15
6.74Ϫ60.36
Ϫ14 to 12
Ϫ14 to 14
Ϫ14 to 14
2376, 0.0308
15
Total reflections, Rint
No. of parameters
Independent reflections, R(σ)
Flack
214, 0.0125
0.61(5)
184, 0.008
0.55(2)
205, 0.0161
0.54(3)
Final R indices [I>3σI] R1
wR2
R indices (all data) R1
wR2
0.0172
0.0391
0.0186
0.0394
0.0110
0.0181
0.0116
0.0181
0.0148
0.0321
0.0152
0.0321
Extinction coefficient
Largest diff. peak and hole /e·A
0.045(5)
ϩ0.88/Ϫ0.55
0.127(4)
ϩ0.93/Ϫ0.63
0.08(1)
ϩ0.72/Ϫ0.52
Ϫ3
˚
a) Lattice parameter from X-ray powder diffraction experiment.
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Z. Anorg. Allg. Chem. 2009, 667Ϫ673

Cadmium Copper Polyphosphide
CSD-420224 (293 K, Crystal 1), CSD-420225 (293 K, Crystal 2),
and CSD-420226 (150 K, Crystal 2).
Table 3. Coordinates and isotropic displacement parameters for
[Cd3Cu]CuP10 at 293 K (crystal 1 and 2) and 150 K (crystal 2).
2
˚
Atom
sof
x
y
z
Uiso /A
Thermal analysis: Thermal analyses (DSC) were performed with a
Netzsch DSC 204t instrument in an nitrogen atmosphere in alu-
minium crucibles. The temperature and enthalpy calibration was
done at different temperatures using mercury, indium, tin, bismuth,
zinc and CsCl at a heating rate of 10 K/min. An accuracy of 1 K
could be estimated from the calibration measurements for onset
values. A temperature range of 173 to 873 K was applied to
[Cd3Cu]CuP10 (Figure 2). At least two consecutive runs were meas-
ured for each sample in order to check the reversibility of the ob-
served effects.
Crystal 1
(293 K)
Cu1
Cd2
Cu2
P1
1
0
0
0
x
x
0.0076(2)
0.0165(1)
0.0165
0.70(2) 0.0965(1) 1/2ϩx
0.30
1
1
0.0965
1/2ϩx
x
0.4908(1)
0.3715(1)
1/2Ϫx 0.0060(2)
1
1
P2
/
/
0.0103(3)
4
4
Crystal 2
(293 K)
Cu1
Cd2
Cu2
P1
1
0
0
0
x
x
0.0077(2)
0.0161(1)
0.0161
0.69(1) 0.0965(1) 1/2ϩx
0.31
1
1
0.0965
1/2ϩx
x
0.4910(1)
0.3713(1)
1/2Ϫx 0.0058(2)
1
1
P2
/
/
0.0104(2)
4
4
Crystal 2
(150 K)
Cu1
Cd2
Cu2
P1
1
0
0
0
x
x
0.0038(1)
0.0131(1)
0.0131
0.79(2) 0.0964(1) 1/2ϩx
0.21
1
1
0.0964
1/2ϩx
x
0.4909(1)
0.3715(1)
1/2Ϫx 0.0034(2)
1
1
Figure 2. A representative DSC measurement of [Cd3Cu]CuP10
recorded during heating at a scanning rate of 10 K·minϪ1 under
nitrogen atmosphere. A broad exothermic effect was found starting
at 573 K featuring a peak maximum at 720 K. No such effect was
observed in the second run.
P2
/
/
0.0077(2)
4
4
˚
Table 4. Selected distances /A of [Cd3Cu]CuP10 at 293 and 150 K.
[Cd3Cu]CuP10
Cu1ϪP1 Cd2/Cu2ϪP2 Cd2/Cu2ϪCd2/Cu2 P1ϪP2
Crystal 1 (293 K) 2.333(1) 2.531(1)
Crystal 2 (293 K) 2.336(1) 2.529(1)
Crystal 2 (150 K) 2.329(1) 2.526(1)
2.859(1)
2.861(1)
2.851(1)
2.192(1)
2.192(1)
2.189(1)
We found one broad, irreversible and exothermic effect staring at
573 K with a peak maximum at about 720 K. This effect was repro-
duceable for independently prepared samples but the start of the
effect and the peak maximum varied by several Kelvin from sample
to sample. A melting of the compounds was not observed during
the measurements up to 873 K, and a X-ray powder phase analysis
was performed after the second DSC run.
perature deviation of less than 0.1 K from the ideal value was
achieved during the measurements.
A correction of Lorentz and polarization effects was applied to the
data. The structure was solved by direct methods [14a] from a data-
set of crystal 1. We have also performed a numerical absorption
correction prior to the refinements [14b], using the measured crys-
tal dimensions determined directly on the diffractometer as starting
values for optimization [14c].
Results and Discussions
[Cd3Cu]CuP10 crystallizes cubic and isostructural to the
¯
[Cu3Sn]CuP10 structure type in space group F43m with a ϭ
˚
10.479(2) A. Table 5 summarizes some crystallographic data
One copper, one mixed occupied copper/cadmium and two phos- of all known [P10]-polyphosphides and gives an overview
phorus sites were identified after structure solution. All crystallo-
graphic data are summarized in Table 2, Table 3 and Table 4.
The heterocluster-position (Cd2/Cu2) showed a significant re-
duction of the occupancy factor if cadmium alone was selected to
occupy this site. A combined refinement of cadmium and copper
on this site, only restricted to a full overall occupancy, resulted in a
reasonable accordance of the refined to the expected composition.
on the lattice parameter variations dependent on the ex-
change of the cluster atoms.
[Cd3Cu]CuP10 crystallizes cubic, space group F43m with
Z ϭ 4 formula units in the cell. One copper forms a fcc cell
with half of the tetrahedral voids filled with an ada-
mantane-like [P10] cage and all octahedral voids occupied
by a [Cd3Cu] heterocluster (Figure 3). This heterocluster is
¯
A reduction of the symmetry to the space group R3m, resulting in characterized by a disorder with a random orientation of
a fourfold twin, with the possibility to achieve an ordered represen-
tation of the heterocluster was tested. No evidence for such an
ordering could be detected. This finding is in accordance with the
results derived from a combined spectroscopic and X-ray scattering
approach for [Ag3Sn]CuP10 [5].
one copper atom per cluster in each of the four possible di-
rections.
This finding is consistent with the structural properties
of the tin containing heteroclusters reported in the
[M3Sn]CuP10 phases. The bond length observed within
the [Cd3Cu] heterocluster is d(Cd2/Cu2ϪCd2/Cu2) ϭ
Further details of the crystal structure investigations are available
from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-
Leopoldshafen (Germany), on quoting the depository number tance of 2.873 A derived from three times the value for cad-
˚
2.859(1) A. This distance is rather close to the averaged dis-
˚
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M. Bawohl, T. Nilges
ARTICLE
Table 5. Lattice parameters and effective ionic and atomic radii of all known [M3X]CuP10 compounds. The radii sum (SumCN6) for all
heterocluster atoms in an anti-prismatic coordination is calculated. Lattice parameter variations closely related to the volume requirements
of the heteroclusters are best described using the atomic instead of the ionic radii.
3
˚
˚
Compound
a /A
V /A
Effective ionic radius
according [15]
Atomic radius [16] and radii sum
for all [M3X] atoms
Lit.
[Cu3Sn]CuP10
10.252(1)
1077.6(1)
Cuϩ
0.77
0.93
3.24
CuCN 6
SnCN 6
SumCN 6
1.186
1.530
5.09
[5]
CN 6
Sn2ϩ
CN 6
SumCN 6
[Cu3Sn]CuP10
[Ag3Sn]CuP10
10.267(1)
10.503(1)
1082.3(1)
1158.0(6)
[2]
[5]
Agϩ
1.15
0.93
4.38
1.37
0.77
0.93
4.69
0.95
0.77
3.62
AgCN 6
SnCN 6
SumCN 6
AuCN 6
CuCN 6
SnCN 6
SumCN 6
CdCN 6
CuCN 6
SumCN 6
1.352
1.530
5.59
1.349
1.186
1.530
5.48
1.453
1.186
5.55
CN 6
Sn2ϩ
CN 6
SumCN 6
[Au2.41Cu0.59Sn]CuP10
[Cd3Cu]CuP10
10.3953(5)
10.4780(2)
1123.34(9)
1146.3(3)
Auϩ
[6]
CN 6
Cuϩ
CN 6
Sn2ϩ
CN 6
SumCN 6
Cd2ϩ
This work
CN 6
Cuϩ
CN 6
SumCN 6
It will be discussed now if the variation of the lattice par-
ameters of [Cd3Cu]CuP10, compared with the other
[M3Sn]CuP10 polyphosphides, is a useful probe to reflect
the metalloid character of the [Cd3Cu] unit. Whereas the
metalloid character was proven by quantum chemical calcu-
lations for [Ag3Sn]P7 and [Au3Sn]P7 [8] and by Mössbauer
spectroscopy for [Ag3Sn]CuP10 [5], a comparable situation
can be estimated for the heteroclusters in all [M3X]CuP10
type compounds. [Cd3Cu]CuP10 crystallizes isostructural to
the tin containing compounds. At least the bonding situ-
ation and the first coordination sphere, an anti-prismatic
coordination of each heterocluster atom by three phos-
phorus atoms of the [P10] units and three cluster atoms, are
almost identical in both cases.
Focussing on the title compound and the related poly-
phosphides it becomes obvious that only the heterocluster
unit itself and the interaction with the polyanion substruc-
ture can significantly influence the lattice parameters in the
present case. The polyanion substructure is rigid and almost
unaffected by the exchange of the heterocluster atoms.
Bond lengths and angles in the [P10] polyanion differ only
marginally and within two times the standard deviation in
most of the cases. Because of its comparable bonding situ-
ation in each ideal-tetrahedral heterocluster of the
[M3X]CuP10 compounds, the radii sum of all atoms is a
suitable and sufficient measure for the correlation of the
lattice parameter change for all [M3X]CuP10 compounds.
The radii sum used here is defined as the sum of all ionic
or atomic radii of the heterocluster atoms corrected to their
coordination sphere. We have applied an ionic and metallic
approach to the heterocluster atoms in terms of the descrip-
tion of the respective radii.
Figure 3. Crystal structure of [Cd3Cu]CuP10. The adamantane-like
[P10] cage fills half of the tetrahedral, and the [Cd3Cu] heterocluster
all octahedral voids of a fcc arrangement build up by copper. The
PϪP distances within the [P10] cages are given for comparison.
Each Cd2/Cu2 position is antiprismatically coordinated by three
cluster and three phosphorus atoms. Displacement parameters at
90 % probability. All literature is cited in the introduction section.
˚
mium d(CdϪCd) ϭ 2.979 A [15a] and one time for copper
˚
d(CuϪCu) ϭ 2.556 A [15b]. It is also located in the bond
˚
length range for CdϪCu bonds of 2.75 to 3.01 A, as ob-
served for instance in the intermetallic compound Cd3Cu4
[12e]. Bond length within the homoatomic [Cd4] cluster in
the intermetallic phases RETCd or RE23T7Cd4 [12aϪd] are
˚
slightly longer ranging from 3.00 to 3.25 A.
Each cluster atom is coordinated anti-prismatically to
their neighbors and the [P10] cage, featuring a distance of
˚
d(Cd2/Cu2ϪP2) ϭ 2.531(1) A between the clusters and the
Taking the ionic representation of the cluster atoms into
account, as stated for the respective ions in a six fold coor-
dination in Table 5, the lattice parameter of [Cd3Cu]CuP10
should be closely related to [Cu3Sn]CuP10. In contrast,
the observed value lies closer to the one found for
[P10] units. In contrast, the bond length d(Cu1ϪP1) between
the isolated cation position and the [P10] unit is 2.3325(9) A,
˚
a well suited value reported for many copper polyphos-
˚
phides like Cu2P7 [d(CuϪP) ϭ 2.27 to 2.40 A] or CuP2
˚
[d(CuϪP) ϭ 2.28 to 2.50 A] [17].
670
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Cadmium Copper Polyphosphide
[Ag3Sn]CuP10. Only the atomic radii, derived from the dis-
tance in the respective elements, and corrected to the coor-
dination number 6, according to the procedure stated in
literature (rCN 6 ϭ rCN 12Ϫ0.090) [16], lead to a straight
forward and linear correlation of lattice parameter and the
radii sum of atoms of the heterocluster.
In the case of the atomic radii its values are corrected to
the radii within the respective coordination sphere (here it
is CN ϭ 6). Figure 4 illustrates the radii sum for all hetero-
clusters in correlation with the lattice parameter of the re-
spective compound. A linear trend can be observed, sub-
stantiating the metalloid character of the heteroclusters.
Following the Zintl concept a formal charge of ϩ7
(3 ϫ Cd2ϩ and Cuϩ) would result for the heterocluster and
ϩ1 for the additional copper cation which can not be
compensated by the [P10] unit only containing six two-
bonded P positions of formal charge Ϫ1. The charge of
the heterocluster must be significantly reduced to derive a
reasonable description of the electronic situation in the
title compound.
Figure 5. Phase analyses of [Cd3Cu]CuP10 before and after the DSC
measurement and results of the cadmium-rich sample. a) Diffracto-
gram of [Cd3Cu]CuP10 (reflections are marked x) prior to the DSC
measurements. A representative crystal of [Cd3Cu]CuP10 is printed
into the top diffractogram b). A slow decomposition was observed
by DSC, resulting in additional reflections in the diffractogram (ϩ).
These reflections are identical to the strongest reflections observed
in the cadmium-rich sample which was annealed at 923 K for 14
days denoted in c) and d). [Cd3Cu]CuP10 is only the minority phase
in this cadmium-rich sample. d) A calculated diffractogram derived
from a preliminary structure determination of the main phase (ϩ)
using the space group C2/m is given. One representative crystal
of this phase and also the measured crystal are given in the last
diffractogram. A vertical line is provided to guide the eyes and to
illustrate the strongest reflection of [Cd3Cu]CuP10. A third un-
Figure 4. Correlation between the sum of the atomic radii of the
cluster atoms in relation to the lattice constant of the isostructural
[M3X]CuP10 compounds.
The open question whether an orientation or substitution
disorder is present in the heterocluster of [Cd3Cu]CuP10 can
not be answered completely at this point. Copper and cad-
mium sometimes show the tendency to occupy the same
sites in intermetallic compounds as shown for instance in known phase (*) is also present in c) and d).
Cd3Cu4 [12e] or the γ-brass compound Cd7.75 Cu5.25 [18].
Also a huge number of ordered binary and ternary inter-
metallics (e.g. Cd5Cu2 [19] or RECu4Cd [20]) are reported
in the literature. Taking the structural features of the tin DSC runs is given in Figure 5. We found additional reflec-
containing polyphosphides into account a substitution dis- tions beside the ones of [Cd3Cu]CuP10 in the diffractogram
order, resulting in the realization of [Cd4] and [Cd2Cu2] which could not be correlated to any known cadmium, cop-
cluster, is at least less probable. Additional experiments per, phosphorus or iodine containing phase. Obviously, the
using local probes like solid state NMR spectroscopy is crystallinity of the decomposition products is low, resulting
needed in the future to finally answer this question.
only in small contributions to the diffractogram. In order
[Cd3Cu]CuP10 is characterized by a surprising reactivity to put some light onto this feature we have tried to identify
upon heating. We found an irreversible, broad and exother- the products to get more information related to this aspect.
mic effect in the DSC experiment which was never observed If the composition is slightly varied towards a cadmium-
before for any of the known [P10] polyphosphides. A X-ray rich one and the synthesis conditions are modified in terms
powder diffraction phase analysis after two consecutive of the applied reaction temperatures (annealing at 923 K
Z. Anorg. Allg. Chem. 2009, 667Ϫ673
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M. Bawohl, T. Nilges
ARTICLE
and quenching instead of 1023 K and a slow cool-down to 573 K to new phases of which at least one contains more
room temperature), the title compound has not been found cadmium than the title compound itself. A first structural
in reasonable amounts any more. A complex mixture of at characterization of the majority phase, which we have found
least three different phases was found instead (see Figure 5) after a preparation using more cadmium compared to the
where the title compound is only the minority compound. ideal composition in [Cd3Cu]CuP10, substantiated the oc-
Both additional phases are possible candidates to be currence of known structure motives found in polyphos-
formed after the decomposition of [Cd3Cu]CuP10 which can phides like Cu2P20 and [M3Sn]P7 (M ϭ Ag, Au).
be estimated from the occurrence of the strongest reflec-
tions in the diffractogram after the DSC experiment. Ad-
Acknowledgement
ditional experiments have to be done to explain the fact
that no thermal effect is observed in the second DSC run
while the majority of [Cd3Cu]CuP10 seemed not to be de-
composed [see b) in Figure 5] after the experiment.
This work was financed by the DFG with the grant NI 1095/1Ϫ1.
Preliminary results of single crystal structure determi-
nations of one of the resulting phases substantiated the oc-
currence of some structural features of the [Ag3Sn]P7 [3a]
and the Cu2P20 structure type [3b]. It was possible to reduce
the space groups to C2/m, Cm or C2 for this phase. A calcu- [3] a) T. Nilges, S. Lange, M. Bawohl, J. M. Deckwart, M. Janssen,
lated powder diffractogram using the space group C2/m was
used to identify the main phase. A full structure determi-
nation is still in progress and will be reported soon. Then
we will be able to give a full description of the phase re-
lations in the present case.
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Cadmium Copper Polyphosphide
ˇ
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Received: December 23, 2008
Published Online: February 13, 2009
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