Beiträge zur Strukturchemie phosphorhaltiger Ketten und Ringe. 11. Die Kristall- und Molekülstrukturen der beiden Konfigurationisomeren des Tetraphospha-silaspiro[2.2]pentans (PBut)2Si(PBut)2

Structural Chemistry of Phosphorus Containing Chains and Rings. 11. Crystal and Molecular Structures of the Two Stereoisomers of Tetraphospha-silaspiro[2.2]pentane (PBu^t)₂Si(PBu^t)₂ The spirocyclic compound 1,2,4,5-tetra-tert-butyl-1,2,4,5-tetraphospha-3-silaspiro[2.2]pentane exists in tow diastereomers of point symmetry 4 and 2. The isomer with symmetry 4 even in the solid crystallizes tetragonally in I4₁/a with a = 1247.0, c = 1505.5 pm and Z = 4. The isomer of fairly exact symmetry 2 crystallizes triclinically in P1 with a = 612.8, b = 996.3, c = 1017.2 pm, α = 75.63, β = 72.38, γ = 88.71° and Z = 1. In this disordered structure the surroundings of Si is slightly distorted due to the influence of the substituents. The (average) bond lengths are (4 , 2): d(Si? P) = 220.09(9), 221.5(5); d(P? P) = 225.5(2), 224.2(5); d(P? C) = 189.4(3), 190(2); d(C? C) = 151.4(4), 152(3) pm. The geometry of the substituents in both isomers is quite normal.