Theoretical studies on the stability of thallium-carbon .sigma.-bonds in aliphatic organothallium compounds

Abstract

Calculations of the electronic structure and bonding in organothallium compounds (TIR, TIR’, T1R2, TIR2+, TIR3, TIR4-, T1R2Br, and TIR’ with R = C H 3 , R‘ = C2H3, or C 2 H ) , in the hydrides ( R = H ) , their dissociation products (CH,, C 2 H 3 , C 2 H , C 2H6 , and TIBr), and TI2 have been carried out. A modified version of Pople’s S C F program GAUS S IANB Z has been used, in which the core electrons on the TI atom are described by a quasi-relativistic [Ptl-core pseudopotential. All bond distances and angles have been optimized with a Fletcher-Powell procedure. SCF-SW-Xa calculations have been carried out to determine the extent of the TI 5d core orbital participation in the T1-C bond. Vibrational frequencies have been calculated f rom the harmonic diagonal S C F valence force field. As a result, the previously undetected molecule T1CH3 is found to be stable with respect to dissociation into TI and CH,. The isolated T1(CH3), molecule is found to possess the expected planar-trigonal (TIC,) structure. It is explained why organothallium chemistry is mainly the chemistry of Tl(II1) in contrast to inorganic thallium chemistry and t h a t TI-TI bonds a r e very weak or do not exist is a relativistic effect.