Abstract

The molecular structure of 1,1,3,3-tetramethylgermacyclobutane has been determined by gas electron diffraction supplemented by ab initio calculations at the HF/6ȁ31G★ and MP2/6-31G★ levels. Structure refinement of a CS model with the differences between symmetry inequivalent Ge-C and C-C bond distances fixed at the HF values yielded the bond distances Ge-C = 197.5(3) and C-C = 156.7(2)pm (endocyclic) and Ge-C = 195.9(3) and C-C = 152.9(2)pm (exocyclic). The endocyclic valence angles are ȢCGeC = 75.3(2)°, ȢGeCC = 89.5(2)° and ȢCCC = 100.7(3)°. The exocyclic ȢCGeC = 108.8(8)°. The central ring is non-planar with a puckering angle of 24(2)°, the barrier to planarity is estimated to be V0 = 4.2(8)kJ molȡ1. Optimisation of the structure of 1,1-dimethylgermacyclopropane at the HF/6-31G★ level yields ȢCGeC valence angles of 47.5° (endocyclic) and 116.2° (exocyclic).

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