Demarcation of the PbFCl and Cu2Sb structure families: Crystal structure re-determinations and refinements of CuMgSb, Cu2Sb, and CuMgAs [German]

摘要

The crystal structures of CuMgSb, Cu2Sb, and CuMgAs have been re-determined and refined from single crystal data, and the structural relationship between CuMgSb (cubic), Cu2Sb (tetragonal) and CuMgAs (orthorhombic) is discussed in detail. CuMgAs does not crystallize in the Cu2Sb type, as assumed until now; but in a new structure type oP24 (Pnma; Z = 8): a = 1346.0(1) pm, b = 395.40(3) pm, c = 739.58(6) pm. The structure is related to Cu2Sb and can be derived from it following the principle of 'chemical twinning'. The re-determined parameters of Cu2Sb are included in a structure field diagram together with additional representatives of the PbFCl type. The structure field can be divided into three regions with the prototypes PbFCl, Cu2Sb, and Fe2As, respectively. The assignment can be related to the predominant type of bonding of each structure. [References: 30]