Cyclische Diazastannylene. - XVIII : Zur Frage der Bindungsbeschreibung in Polyedern des Typs Sn4X3Y : die Kristall- und Molekülstrukturen von Sn4(NtBu)4 und Sn4(NtBu)3O

Abstract

Crystals of Sn4(NtBu)4 (1) are monoclinic, space group P2(1/c), with cell constants a=1038.9(4), b=1468.3(5), c=1698.8(5) pm, beta=91.6(1)° and Z=4, while those of Sn4(NtBu)3O (2) are triclinic, space group P(-)1, with dimensions a=1293.0(5), b=1027.1(5), c=1716.7(9) pm, alpha=90.9(1), beta=102.5(1), gamma=107.0(1)° and Z=4. The molecules 1 are held together by von-der-Waals forces, whereas two molecules 2 interact in the crystal by weak O --> Sn donor bonds (290-332 pm) forming dimers. The outstanding structural elements of 1 and 2 are the Sn4N4 and Sn4N3O polyhedra, which can be described by two interpenetrating tetrahedra of tin atoms and of nitrogen or nitrogen and oxygen atoms forming a distorted cube, which approaches (-)43m symmetry in the case of 1 and 3m for 2. Characteristic distances are in 1: Sn-N 220.2 pm, in 2: Sn-N 221.3 pm and Sn-O 213.2 pm. An almost ionic bonding model and two covalent models are discussed on the basis of the structural data including Sn4(NtBu)3OAlMe3.