COMPARISON BETWEEN POST-HARTREE-FOCK AND DFT METHODS FOR THE STUDY OFSTRENGTH AND MECHANISM OF CLEAVAGE OF HG-C BOND

A parallel MP2 and DFT study was performed for mercury dihalides and f or representative organomercury compounds including a Hg-C bond. From a methodological point of view, medium-size basis sets provide reliabl e general trends for a number of properties already at the HF level. H owever, quantitative results can only be obtained including correlatio n energy by post-Hartree-Fock (even at the MP2 level) or density funct ional models and adding f-polarization functions on Hg. At this level, geometrical parameters are sufficiently accurate for most purposes an d reliable thermodynamic data can be obtained using isodesmic reaction s. The advantage of the DF approach resides, besides the shorter compu tation times, in the lower dependence of the results on the basis set. From a more general point of view, all the computations indicate that Hg-C bond breaking is favored, decreasing the electronegativity of fu rther substituents. We have next investigated the reaction mechanism f or cleavage of the Hg-C bond by halogenic acids. Our results show that the reaction occurs through a one-step mechanism in which, however, b ond forming and breaking are not completely synchronous. (C) 1997 John Wiley & Sons, Inc.