Furyl- and thienyl-mercury derivatives studied by means of ultraviolet photoelectron spectroscopy. Evidence for the participation in bonding of the vacant 6pπ orbitals of mercury in bis-2-furyl- and bis-2-thienyl-mercury

Abstract

The ultraviolet photoelectron spectra (UPS) of several furyl- and thienyl-mercury derivatives have been recorded. The analysis of the furan-like π₂ and π₃ molecular orbitals (MOs) indicated that in bis-2-furylmercury there is a small charge-transfer interaction between the filled ring π orbitals and the empty 6pπ mercury atomic orbitals, that this interaction is larger than in the corresponding bis-3-furyl derivative, and, for both compounds, larger than the interaction with the 5d atomic orbitals of mercury. This conclusion is supported by X-ray photoelectron spectral (XPS) data and iterative extended Hückel MO (IEHMO) calculations, and applies equally well to the corresponding thiophen derivatives. The electron-releasing inductive effect of mercury, in these compounds, turned out to be similar to or slightly larger than that of a methyl group. The CH₂HgCl substituent exerts a hyperconjugative destabilization on the ring π₂ and π₃ MOs via the C–Hg σ bond. This effect is, however, smaller than that exerted on benzene and ethylene. The HgCl substituent was found to be slightly electron-withdrawing.