Cyclische Diazastannylene, XVIII [1]Zur Frage der Bindungsbeschreibung in Polyedern des Typs Sn4X3Y:Die Kristall-und Molekülstrukturen von Sn4(NtBu)4 und Sn4(NtBu)3O / Cyclic Diazastannylenes, XVIII [1]Bonding Description in Polyhedra of the Sn4X3Y-Type:The Crystal and Molecular Structures of Sn4(NtBu)4 and Sn4(NtBu)3O

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Abstract
Crystals of Sn4(NtBu)4 (1) are monoclinic, space group P21/c, with cell constants a = 1038.9(4), b = 1468.3(5), c = 1698.8(5) pm, β = 91.6(1)° and Z = 4, while those of Sn4(NtBu)3O (2) are triclinic, space group P 1̄, with dimensions a = 1293.0(5), b = 1027.1(5), c = 1716.7(9) pm, α = 90.9(1), β = 102.5(1), γ = 107.0(1)° and Z = 4. The molecules 1 are held together by van-der-Waals forces, whereas two molecules 2 interact in the crystal by weak 0→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 4̄3 m 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.