Alkoxistannate. - II : Tri(tert-Butoxi)alkalistannate(II) : Darstellung und Strukturen

Tri(terf-butoxi)alkalistannates (M (O rBu)3 Sn, M = Li, Na, K, Rb, Cs) are obtained by reaction of alkali-fert-butanolates with tindi-terf-butoxide. If M equals Li or Na (1, 2) molecular com ­ pounds are formed, which consist of two formula units. 1 crystallizes in a monoclinic cell (space group P2[/c; a = 966.5(3), b = 1819(1), c = 1014(1) pm./3 = 107.1(1)°, Z = 4); 2 is triclinic (space group PI; a = 1041(1), b = 2046(1), c = 1033(1) pm. a = 92.3(2), ß = 118.6(1), y = 108.3(3)° and Z = 4). The m olecules 1 and 2 are closely related structurally despite their different space groups. The common structural feature is a Sn2 O fiM 2 cage, which is built of two seco-norcubane Sn2 M 2 0 , units, sharing a M 2 0 2 four-membered ring. Characteristic distances are: 1: Sn—O = 209.3, L i-O = 193.0 and 211.6 pm, 2: S n -O = 210.5, N a -O = 227.4 and 240.7 pm. The ter/-butoxistannates of K, Rb and Cs (3, 4, 5) all crystallize in the orthorhombic crystal system, space group P 2 12 ,2 1 (cell constants o f 3: a = 1907(1), b — 1060(1), c — 896(1) pm, Z = 4). Contrary to the lithiumand sodium derivates 3, 4 and 5 have a polymeric structure. The one dimensional polymer consists of distorted trigonal bipyramidal S n 0 3M “cages” (substituted at the oxygen atoms by tertbutyl groups), which align in a way to allow the metal atom to have a five-fold oxygen coordina­ tion. The tin atoms have trigonal pyramidal coordination. While the tin-oxygen bond lengths are essentially invariant (average value 206.7 pm), the potassium-oxygen distances range from 256.4(5) pm to 318.8(6) pm.