The Molecular Structures of Dimethyl-, Diethyl- and Dipropylzinc Determined by Gas Phase Electron Diffraction. Normal Coordinate Analysis and ab initio Molecular Orbital Calculations on Dimethylzinc.

Abstract

Me2Zn, Et2Zn and Pr2Zn have been investigated by gas phase electron diffraction. The Zn-C bond distance in Me2Zn, 193.0(2) pm, is significantly smaller than in Et2Zn and Pr2Zn, 195.0(2) and 195.2(3) pm, resp. The valence angle ZnCC is 114.5(3) Deg in Et2Zn and 114.5(5) Deg in Pr2Zn. 74(4)% Of the alkyl chains in Pr2Zn are in a synclinal conformation suggesting the presence of a weak attraction between the Zn atom and the terminal Me group. Least squares refinement of a relatively simple valence force field for Me2Zn yielded force consts. that reproduce the frequencies of the normal modes according to the latest assignment to the nearest cm-1. The structure of Me2Zn has been fully optimized by ab initio mol. orbital calcns. with a double zeta basis. The optimal structure is in reasonable agreement with the exptl. results, and the orbital energy sequence in agreement with the published PE spectrum. Population anal. indicates that the 3d electrons of Zn must be regarded as non-binding and the Zn-C bond as pure s-bond. [on SciFinder (R)]