An electron diffraction study of the molecular structure of gaseous cyclobutylgermane

The molecular structure and conformation of cyclobutylgermane have been determined by gas-phase electron diffraction. Like its counterpart cyclobutylsilane (CBS) it possesses quasi-equatorial and quasi-axial conformers. The most interesting aspect of the structure of CBG is the influence of the germyl group on the ratio of equatorial to axial conformers. The predominance of the quasi-equatorial conformer (ΔG = 3.1(1) kJ mol⁻¹), the near equality of the skeleton C---C bond lengths (C---C = 1.557(3)A) (r_a value) and the values of the puckering angles for the equatorial angles form and the axial one of 25.3(3.1)° and −20.4(3.6)° respectively, all support the predictions made by Jonvik and Boggs concerning the correlation between electronegativity and structural parameters in four-membered rings. From a consideration of these predictions, a comparison of the most prominent structural factors in CBG and cyclobutylsilane indicates that the germanium atom is more electronegative than silicon. This result could be considered as the first structural evidence for the previously postulated inversion of the electronegativity order within group IV.