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 A(12)(I) M-17(IV) (A(1)=Na, K, Rb, Cs; M-IV=Si, Ge, Sn) and A(4)(I) M-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(4)Pb(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)degrees, R1=0.0674/0.0674) the Pb atoms form isolated Wade nido clusters [Pb-9](4-) of approximate C-4v 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 K12Si17 (monoclinic, space group P2(1)/c, a = 2368.9(3), b 1357.2(2), c = 4450.9(6), beta = 91.248(4)degrees, Z = 4) and Rb12Sn17 (orthorhombic, space group P2(1)2(1)2(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 [Mg-9](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 A(12)(I) M-17(IV) have been prepared, and both spectroscopic and preliminary X-ray crystallographic data could be obtained for them. (C) 2003 Elsevier B.V. All rights reserved.