Synthesis and crystal structure of the tetrelides A12M17 (A=Na, K, Rb, Cs; M=Si, Ge, Sn) and A4Pb9 (A=K, Rb)

A series of different compounds of stoichiometries A12IM17IV (AI=Na, K, Rb, Cs; MIV=Si, Ge, Sn) and A4IM9IV (AI=K, Rb; MIV=Pb) were synthesized from the elements and their crystal structures determined on the basis of single crystal X-ray data. In the compounds A4Pb9 (A=K/Rb; monoclinic, space group P21/m, a = 960.1(9)/989.4(9), b = 1319.0(12)/1340.6(12), c = 1582.3(14)/1624.3(14) pra, 103.19(2)/103.23(2)DG, R1 =0.0674/0.0674) the Pb atoms form isolated Wade nido clusters [Pb9]4- of approximate C4v symmetry (monocapped square antiprisms), which are arranged in a hexagonal closed packing and are separated by the A cations. Similar cluster anions M94- (M = Si, Sn) are present in the compounds Kl2Sil7 (monoclinic, space group P21/c, a = 2368.9(3), b = 1357.2(2), c = 4450.9(6), *b = 91.248(4)DG, Z = 4) and Rb12Sn17 (orthorhombic, space group P212121, a = 1504.1(6), b = 1539.34(12), c = 2147.8(2) pm, Z = 4) which can formally be described by an ionic decomposition into K/Rb cations and two Zintl anions [M4]4- (M = Si, Sn; isosteric with white phosphorus) and one [M9]4- cluster. The two compounds represent examples of hierarchical variants of the Laves phases MgZn2 and MgCu2, respectively. A number of additional members of the series A12IM17IV have been prepared, and both spectroscopic and preliminary X-ray crystallographic data could be obtained for them.