SIS2 ISOSTRUCTURAL ANIONS [SIP2], [GEAS2] AND [SNAS2] IN ALKALINE COMPOUNDS - P(2-) AND AS(2-)

K2[GeAs2], Rb2[SnAs2], Cs2[SiP2], Cs2[SiAs2] and Cs2[SnAs2] were prepared from molten mixtures of the elements under an argon atmosphere in Al2O3 crucibles. The compounds form needle-shaped crystals, which are sensitive to moisture. The structures are of the K2[SiP2] type and contain the polyanionic chains infinity 1[SiP4/2(2-)], infinity 1[SiAs4/2(2-)], infinity 1[GeAs4/2(2-)] and infinity 1[SnAs4/2(2-)] composed of edge-sharing tetrahedra, isoelectronic and isostructural with SiS2. The structures were refined from X-ray single-crystal data: space group Ibam (No. 72), Z = 4. K2[GeAs2]: a = 1329.2(4) pm, b = 702.8(3) pm, c = 654.8(3) pm Rb2[SnAs2]: a = 1397.4(4) pm, b = 745.4(3) pm, c = 694.2(3) pm Cs2[SiP2]: a = 1412.7(4) pm, b = 746.2(3) pm, c = 619.6(3) pm Cs2[SiAs2]: a = 1442.5(4) pm, b = 757.1(3) pm, c = 642.0(3) pm Cs2[SnAs2]: a = 1465.7(4) pm, b = 773.3(3) pm, c = 695.3(3) pm