Molecular Structure of Trichloroethenylgermane, CH2═CH−GeCl3, as Studied by Gas-Phase Electron Diffraction. Experimental Determination of the Barrier of Internal Rotation of the Trichlorogermyl Group Supplemented with Quantum Chemical Calculations on CH2═CH−MX3 (M = C, Si, Ge, Sn, and X = H, Cl)

Abstract

The molecular structure of trichloroethenylgermane, CH(2)=CH-GeCl(3), has been determined by electron diffraction and supported by quantum chemical calculations on CH(2)=CH-MX(3) (M = C, Si, Ge, Sn and X = H, Cl). An equilibrium syn conformation with C(s) symmetry is obtained both experimentally and theoretically where one of the Ge-Cl bonds eclipses the C=C bond. The barrier of internal rotation about the C-Ge bond is determined to be V(3) = 5.3(7) kJ mol(-1) using a dynamic model to simulate the internal motion. The most important structure parameters (estimated r(e)/A and angle/degree) are: r(C-Ge) = 1.911(5), r(C=C) = 1.345(5), r(Ge-Cl7) = 2.122(2), <C=C-Ge = 120.4(5), <C-Ge-Cl7 = 111.0(2), and <Cl7-Ge-Cl8) = 109.4(5) where the Cl7 atom is in the C=C-Ge plane and the Cl8 atom is out of the C=C-Ge plane. Uncertainties are estimated total standard deviations (sigma(tot)) given as: sigma(tot) = [sigma(2)(scale) + (2sigma(lsq))(2)](1/2) for bond lengths where sigma(scale) = 0.001r and sigma(lsq) is the least-squares standard deviation using a diagonal weight matrix and sigma(tot) = 2sigma(lsq) for the other parameters. The assignment of some of the fundamental frequencies has been discussed. The internal agreement between the calculated molecular geometry obtained from B3LYP and MP2(F) using the cc-pVQZ basis set and to the experimental geometry is not good, whereas the molecular geometry obtained from a CCSD/cc-pVTZ calculation is in very good agreement with experimental geometry. This investigation shows that the gas electron-diffraction method is capable of determining the rotational barrier for small suitable molecules with acceptable accuracy.