Cu4.35Cd1.65As16: the first polyarsenic compound in the Cu–Cd–As system

Oliver Osters; Tom Nilges

doi:10.1107/S1600536811042127

. 2011 Oct 22;67(Pt 11):i62. doi: 10.1107/S1600536811042127

Cu_4.35Cd_1.65As₁₆: the first polyarsenic compound in the Cu–Cd–As system

Oliver Osters ^a, Tom Nilges ^a,^*

PMCID: PMC3246907 PMID: 22219727

Abstract

The first polyarsenic compound in the Cu–Cd–As system was obtained by solid-state reaction of the elements and has a refined composition of Cu_4.35 (2)Cd_1.65 (2)As₁₆ (tetracopper dicadmium hexadecaarsenide). It adopts the Cu₅InP₁₆ structure type. The asymmetric unit consists of one Cu site, a split Cu/Cd site and four As sites. The polyanionic structure can be described as being composed of As₆ rings in chair conformations which are connected in the 1-, 2-, 4- and 5-positions. The resulting layers evolve along the c axis perpendicular to the ab plane. One Cu atom exhibits site symmetry 2 and is tetrahedrally coordinated by four As atoms. The other Cu atom, representing the split site, and the corresponding Cd atom have different coordination spheres. While the Cu atom is tetrahedrally coordinated by four As atoms, the Cd atom has a [3 + 1] coordination with a considerably longer Cd—As distance.

Related literature

For Cu₅InP₁₆, see: Lange et al. (2008 ▶). For related polyphosphides, see: Pöttgen et al. (2006 ▶). For polyarsenides, see: Bauhofer et al. (1981 ▶); Jeitschko et al. (2000 ▶); Emmerling & Röhr (2002 ▶); Emmerling et al. (2004 ▶); Hönle et al. (2002 ▶). For binary Cu–Cd phases, see: Brandon et al. (1974 ▶); Kreiner & Schaepers (1997 ▶); von Heidenstamm et al. (1968 ▶). For related structures, see: Mansmann (1965 ▶); Clark & Range (1976 ▶). For crystallographic background, see: Becker & Coppens (1974 ▶).

Experimental

Crystal data

Cu_4.35Cd_1.65As₁₆
M _r = 1660.8
Monoclinic,
a = 11.8324 (6) Å
b = 10.4423 (4) Å
c = 8.0903 (4) Å
β = 110.480 (4)°
V = 936.44 (8) Å³
Z = 2
Mo Kα radiation
μ = 34.73 mm⁻¹
T = 293 K
0.030 × 0.020 × 0.004 mm

Data collection

Stoe IPDS 2T diffractometer
Absorption correction: numerical (X-AREA; Stoe & Cie, 2011 ▶) T _min = 0.205, T _max = 0.785
12811 measured reflections
1268 independent reflections
1113 reflections with I > 3σ(I)
R _int = 0.053

Refinement

R[F ² > 2σ(F ²)] = 0.036
wR(F ²) = 0.072
S = 1.83
1268 reflections
56 parameters
Δρ_max = 1.50 e Å⁻³
Δρ_min = −1.67 e Å⁻³

Data collection: X-AREA (Stoe & Cie, 2011 ▶); cell refinement: X-AREA; data reduction: X-AREA; program(s) used to solve structure: Superflip (Palatinus & Chapuis, 2007 ▶) embedded in JANA2006 (Petřiček et al., 2006 ▶); program(s) used to refine structure: JANA2006; molecular graphics: DIAMOND (Brandenburg & Putz, 2005 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811042127/wm2539sup1.cif

e-67-00i62-sup1.cif^{(12.5KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811042127/wm2539Isup2.hkl

e-67-00i62-Isup2.hkl^{(54.1KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Cu1—As1	2.4254 (9)
Cu1—As3	2.3931 (9)
Cu2—As2	2.516 (5)
Cu2—As3	2.501 (5)
Cu2—As4ⁱ	2.589 (6)
Cu2—As4ⁱⁱ	2.524 (7)
Cd2—As2	2.856 (5)
Cd2—As3	2.516 (5)
Cd2—As4ⁱ	2.475 (5)
Cd2—As4ⁱⁱ	2.569 (6)

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

The authors thank the German Science Foundation (DFG) for the kind support of this project within the SPP 1415.

supplementary crystallographic information

Comment

Besides the plethora of known polyphosphides (Pöttgen et al., 2006) only few polyarsenides are known up to date (Bauhofer et al., 1981; Jeitschko et al., 2000; Emmerling & Röhr, 2002; Emmerling et al., 2004; Hönle et al., 2002).

The title compound Cu_4.35 (2)Cd_1.65 (2)As₁₆ is the first representative of a polyarsenide adopting the Cu₅InP₁₆ structure type (Lange et al., 2008). In accordance to the situation in Cu₅InP₁₆ where Cu and In are occupying the same site, a similar behavior is observed for the title compound, but here with a Cu/Cd split position. Mixing of Cu and Cd on one site is a common feature in intermetallic compounds and has been observed for instance for Cd₃Cu₄ (Kreiner & Schaepers, 1997) and Cd₈Cu₅ (von Heidenstamm et al., 1968; Brandon et al., 1974).

Cu—As distances in Cu_4.35 (2)Cd_1.65 (2)As₁₆ range from 2.3931 (9) Å to 2.589 (6) Å and are comparable with the distances of 2.404 (1) Å to 2.590 (1) Å in Cu₃As (Mansmann, 1965). The As—As distances in Cu_4.35 (2)Cd_1.65 (2)As₁₆ are between 2.4242 (8) Å and 2.4644 (10) Å, in good accordance with the As—As distances in NdFe₄As₁₂ (2.428 Å - 2.499 Å) (Jeitschko et al., 2000). Cd—As distances are present between 2.475 (5) Å and 2.856 (5) Å which is consistent with values found for CdAs (2.473 (2) Å - 2.868 (2) Å) (Clark & Range, 1976).

Experimental

Cu_4.35 (2)Cd_1.65 (2)As₁₆ was prepared by a solid state reaction from the elements Cu (ChemPur, shot, 99.999%), Cd (ChemPur, granules, 99.9999%) and As (ChemPur, pieces, 99.9999%). Arsenic was purified by sublimation in evacuated silica ampoules using a temperature gradient of 573 K to room temperature to separate As₂O₃ from the bulk-As and at 873 K to 573 K to sublimate As directly. The purified As was stored under protection gas atmosphere prior to use. The starting materials were reacted in stoichiometric amounts according the reported composition at 753 K for 7 days followed by a homogenization step by grinding. The procedure was repeated two times to finalize the formation of the title compound. Single crystals of suitable size could be separated from the bulk phase.