Deviation from tetrahedral geometry in Me(2)GeCl(2): crystal structure of a model compound and insight from ab initio calculations.

The molecular structure of Me(2)GeCl(2), and the value of the C-Ge-C angle in particular, was studied by ab initio quantum calculations to examine the deviation of this molecule from ideal geometry in the gas phase and in the crystalline state. The results show that, in the crystal, intermolecular interactions do have a large influence on the geometry of the molecule. An experimental value of 121.2 +/- 0.2 degrees is found for the C-Ge-C angle in the crystal structure of dichlorodi(2-phenethyl)germane, and it provides the first crystallographic evidence for the deviation from tetrahedral geometry. This molecule crystallizes in the monoclinic space group P2(1)/c, with a = 9.2079(2) A, b = 19.5396(4) A, c = 9.7845(2) A, beta = 114.217(1) degrees, and Z = 4. Calculations show that the conformation of the organic substituents has a sizable effect on the local geometry of the Ge-atom. Analysis of the distribution of the electron density suggests that the larger value of C-Ge-C in Me(2)GeCl(2) compared to the equivalent but smaller angle in Me(2)CCl(2) is indirectly the result of the higher ionic character of the bonds in the former molecule.