ABINITIO AND SEMIEMPIRICAL STUDIES OF ELECTRON-TRANSFER AND SPECTRA OF BINUCLEAR COMPLEXES WITH ORGANIC BRIDGES

Electron transfer and spectra of binuclear complexes of the general type L5M-B-M'L5 are studied theoretically. The ab initio CASSCF method is applied in the case of the (NH3)5Ru-pyz-Ru(NH3)5(4+/5+/6+) where pyz is pyrazine. In the 5+ case we confirm the accepted interpretation that there is a strong xz coupling via the pyz pi-orbitals with delocalized valencies. In the 6+ case, however, we calculate a very weak antiferromagnetic coupling between the metal ions, in agreement with the experiments. Semi-empirical CNDO/S and tight-binding methods are used for the larger systems also studied: L5Ru2+-B-Ru3+L5 and L5Ru2+-B-Co3+L5, B = dipyridine (dip), dipyridine methane (dipM), or dimethyl dipyridine (DMdip); in some cases with other ligands L than NH3. The results correlate reasonably well with spectroscopical data and experimental electron transfer rates.