INVESTIGATIONS ON THE ELECTRONIC INFLUENCE OF ORGANYL LIGANDS .9. TRANSINFLUENCE IN MERCURY ORGANYL COMPOUNDS - A PSEUDOPOTENTIAL ABINITIO STUDY

Pseudopotential ab initio-calculations at the SCF level with partial geometry optimization have been performed on mercury organyl compounds L-Hg-CH3 (L = C = CH, CH = CH2, CH2-CH3, CH3). The trans-influence of L on the Hg-CH3 bond increases, i.e. bond strength decreases, if the carbon atom bonded to Hg is itself only weakly bonded to its neighbouring carbon (CH2-CH3 vs. CH = CH2 vs. C = CH) or if the chain length of L increases (CH2-CH3 vs. CH3). This bond weakening leads to an elongation of the Hg-CH3 bond distance as a result of geometry optimization. The results agree with coupling constants 1J(Hg-199-C-13) known from experiment. The calculations show that a stronger trans-influence of L is connected with larger charge transfer to the Hg-CH3 fragment, especially with an increasing s population on mercury, which for its part is responsible for lower values of the coupling constants. The amount of trans-influence can be traced back to the electronegativity of the trans-influencing group.