Crystal structures of hexachalcogeno-hypodiphosphates of magnesium and zinc

Five chalcogeno-hypodiphosphates were synthesized and investigated by single crystal X-ray methods. Mg2P2S6 (C2/m; a = 6.085(1) b = 10.560(2), c 6.835(l) Angstrom, beta = 106.97(3)degrees; Z = 2) crystallizes with the Fe2P2S6 type structure, whereas Mg2P2Se6 (a = 6.404(l), c = 20.194(4) Angstrom) and Zn2P2Se6 (a = 6.290(3), c = 19.93(2) Angstrom) build up the Fe2P2Se6 type (R (3) over bar; Z = 3). The structures are characterized by closest packings of sulfur (selenium) with Mg2+ (Zn2+) ions and P-2 pairs in half the octahedra - analogous to the CdCl2 and CdI2 type, respectively In Mg2P2S6 half the Mg2+ ions can be substituted by Ag+ ions resulting in Ag2MgP2S6 (C2/n; a = 6.364(1) b = 10.975(2) c = 13.999(3) Angstrom, beta = 108.29(3)degrees; Z = 4). In this compound the Ag+ ions are disordered and located in the octahedra originally occupied by Mg2+ ions. in Mg2P2Se6 an analogous substitution by K+ ions leads to the compound K2MgP2Se6 (P2(1)/n; a = 6.546(l), b = 12.724(3), c = 7.599(2) Angstrom, beta = 103.02(3)degrees; Z = 2) with K2FeP2S6 type structure. The structure is characterized by columns of alternating face-sharing Se octahedra (centered by Mg) and trigonal antiprisms (centered by P-2 pairs) along [100]. The columns are interconnected by inserted K+ ions.