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 well 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 ruthenium 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 oxidation state of 2+ or 3+. Geometry optimizations at both ab initio and semiempirical INDO levels are presented. The proposed parametrization of the INDO model reproduces both the geometry and the absorption spectra of ruthenium complexes with good accuracy. Bond length changes upon changing the oxidation state of the metal are not fully reproduced. 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.