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

Abstract

Tri(tert-butoxi)alkalistannates (M(OtBu)3Sn, M=Li, Na, K, Rb, Cs) are obtained by reaction of alkali-tert-utanolates with tindi-tert-butoxide. If M equals Li or Na (1,2) molecular compounds are formed, which consist of thwo formula units. 1 crystallizes in a monoclinic cell (space group P21/c; a=966.5(3), b=1819(1), c=1014(1) pm, beta=107.1(1)°, Z=4); 2 is triclinic (space group P(-)1, a=1041(1), b=2046(1), c=1033(1) pm, alpha=92.3(2), beta=118.6(1), gamma=108.3(3)° and Z=4). The molecules 1 and 2 are closely related strucrurally despite their different space groups. The common structural feature is a Sn2O6M2 cage, which is built of two seco-norcubane Sn2M2O3 units, sharing a M2O2 four-membered ring. Characteristic distances are: 1: Sn-O=209.3, Li-O=193.0 and 211.6 pm, 2: Sn-O=210.5, Na-O=227.4 and 240.7 pm. The tert-butoxi-stannates of K, Rb and Cs (3,4,5) all crystallize in the orthorhombic crystal system, space group P2(1)2(1)2(1) (cell constants of 3: a=1907(1), b=1060(1), c=896(1) pm, Z=4). Contrary to the lithium- and sodium derivates 3, 4 and 5 have a polymeric structure. The one dimensional polymer consists of distorted trigonal bipyramidal SnO3M "cages" (substituted at the oxygen atoms by tert-butyl groups), which align in a way to allow the metal atom to have a five-fold oxygen coordination. 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.