SOLVENT EFFECT ON THE OPTICAL-PROPERTIES OF [(NH3)(5)RU-PYRAZINE](-INITIO CALCULATIONS(M) (M=2,3) COMPLEXES BY AB)

We have carried out a study, by ab initio methods, of the solvent effe ct on [(NH3)(5)Ru-pyrazine](m+) (m=2 and 3) complexes, which are of in terest as basic units of metallic chains with potential application in molecular electronics and photonics. We have performed multireference configuration interaction (CI) calculations in which solvent effects are included by the Polarizable Continuum Model. A new method for the estimate of the size of the cavities in this approach, which has prove n to be suitable for the specific case under study, is also proposed. Our calculations account for the red shift of the metal-to-ligand char ge transfer band, observed experimentally for the Ru(LI) compound as t he solvent donor number increases, and furnish an explanation with a s olid theoretical foundation. For the Ru(III) compound we find that the ground state configuration is different in vacuum and in electron don or solvents. (C) 1998 American Institute of Physics. [S0021-9606(98)31 243-X].