Synthesis and crystal structure of the tetrelides A 12M 17 (A=Na, K, Rb, Cs; M=Si, Ge, Sn) and A 4Pb 9 (A=K, Rb)

Abstract

A series of different compounds of stoichiometries A I 12M IV 17 (A I=Na, K, Rb, Cs; M IV=Si, Ge, Sn) and A I 4M 9 IV (A I=K, Rb; M IV=Pb) were synthesized from the elements and their crystal structures determined on the basis of single crystal X-ray data. In the compounds A 4Pb 9 (A=K/Rb; monoclinic, space group P2 1/ m, a=960.1(9)/989.4(9), b=1319.0(12)/1340.6(12), c=1582.3(14)/1624.3(14) pm, 103.19(2)/103.23(2)°, R1=0.0674/0.0674) the Pb atoms form isolated Wade nido clusters [Pb 9] 4− of approximate C 4 v symmetry (monocapped square antiprisms), which are arranged in a hexagonal closed packing and are separated by the A cations. Similar cluster anions M 9 4− (M=Si, Sn) are present in the compounds K 12Si 17 (monoclinic, space group P2 1/ c, a=2368.9(3), b=1357.2(2), c=4450.9(6), β=91.248(4)°, Z=4) and Rb 12Sn 17 (orthorhombic, space group P2 12 12 1, 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 [M 4] 4− (M=Si, Sn; isosteric with white phosphorus) and one [M 9] 4− cluster. The two compounds represent examples of hierarchical variants of the Laves phases MgZn 2 and MgCu 2, respectively. A number of additional members of the series A I 12M IV 17 have been prepared, and both spectroscopic and preliminary X-ray crystallographic data could be obtained for them.