AB-INITIO AND SEMIEMPIRICAL CALCULATIONS OF GEOMETRY AND ELECTRONIC-SPECTRA OF RUTHENIUM ORGANIC-COMPLEXES AND MODELING OF SPECTROSCOPIC CHANGES UPON DNA-BINDING

A new parameter set for the INDO model is proposed for ruthenium as we ll as a general way to obtain parameters for any transition metal. The ionic state bf the transition metal rather than the atomic state has been used to obtain ionization potentials. A rather large series of ru thenium complexes are treated in this work, ranging from [Ru(NH3)(6)]( 2+) to [Ru(phen)(2)dppz](2+) (phen = phenanthroline, dppz = dipyrido[3 ,2-a:2',3'-c]phenazine) and the so-called Creuz-Taube ion ([Ru(NH3)(5) -pyrazine-Ru(NH3)(5)](4+/5+)). In all the complexes, Ru has a formal o xidation state of 2+ or 3+. Geometry optimizations at both ab initio a nd semiempirical INDO levels are presented. The proposed parametrizati on of the INDO model reproduces both the geometry and the absorption s pectra of ruthenium complexes with good accuracy. Bond length changes upon changing the oxidation state of the metal are not fully reproduce d. The ab initio calculations predict Ru-N bond lengths that are 0.1-0 .15 Angstrom too long compared to observations. The corresponding bond lengths are calculated in better agreement with observations with the INDO model. The effect upon DNA binding on the calculated spectrum of the [Ru(phen)2dppz](2+) complex was investigated. The DNA binding was modeled by a molecular mechanics energy minimization of a [Ru(phen)(2 )dppz](2+)-poly(dA-dT) complex.