TRIOXORHENIUM AND TRIOXOTECHNETIUM AS STRONG ACCEPTOR GROUPS .3. CHARGE-TRANSFER AND BONDING ENERGETICS IN O(3)M-M(CO)(5) (M=RE,TC)

Ab initio SCF, two-configuration (TC) SCF, and CI calculations have be en carried out to investigate the bonding potentialities of Re(VI) in trioxorhenium with Re(O) in Re(CO)(5). Calculations show that the elec tron-withdrawing character of ReO3 makes the hypothetic O3Re-Re(CO)(5) binuclear complex a highly polar molecule. The charge transfer toward trioxorhenium (0.534 e) is not so large, however, as in O3Re-ReCl2(dm pm)(2), the only bimetallic complex characterized to date with,ReO3. I n both O3Re-Re(CO)(5) and O3Re-ReCl2(dmpm)(2), the metal-metal couplin g can be expressed in terms of a sigma donation from the most oxidized rhenium atom to the least oxidized one. The topological analysis of t he Laplacian distribution of density shows that the bonding of the ReO 3 fragment is mostly ionic. The critical points of the Laplacian distr ibution characterized along the metal-metal bond axis are typical of a a donation, but also evidence some covalent character. The energy ass ociated with a homolytic dissociation is computed to be 271 kJ mol(-1) , accounting for the geometrical relaxation of the ligands. This value is larger than the Re-L bond energies previously computed for various types of O3Re-L molecules. An investigation carried out on O3Tc-Tc(CO )(5) leads to similar results.