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

[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 polyphosphides using CuI as the mineralizer species. The title compound crystallizes cubic in the space group F4̄3m (No. 216), with a = 10.479(2) Å and V = 1150.9(4) ų. It is isostructural to the tin containing coinage-metal polyphosphides [M₃Sn]CuP₁₀ with M = 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 measurements substantiated the refined composition within the standard deviation of the experiment. A slow decomposition of [Cd₃Cu]CuP₁₀ was proven by DSC measurements and annealing 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 structure determination of the main phase after decomposition 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.