Electronic structure and spectra of binuclear bridged nitrosyl ruthenium complexes (original) (raw)

2007, Russian Journal of Coordination Chemistry

The interest in the nitrogen(II) oxide chemistry, which has skyrocketed in recent decades, is due to the discovery of its fundamental role in biological processes in mammals , which stimulated the intense search for new therapeutic drugs capable of increasing or decreasing the NO content in organs and tissues. Considerable attention is paid to thermally stable compounds, which may give off a nitrogen(II) oxide molecule upon controlled exposure to light. Nitrosyl ruthenium complexes are among the most promising compounds in this respect. Previously, the electronic spectra of nitrosyl ruthenium complexes containing N-heterocyclic [5] and macrocyclic ligands, [ Ru ( NO )( Salen )( X )] n (X = Cl, H 2 O ; n = 0, 1) and [Ru(NO)(P)(ONO)] (Salen is the N , N ′ -ethylenebis(silicylideneiminate)dianion and P is the porphyrinatedianion), were calculated by the TDDFT and CINDO-CI methods . Lower electronically excited states ( EES ) were found to correspond to transitions within the {RuNO} group. In the case of complexes with strong donor ligands, these also include the admixed transition due to charge transfer from these ligands to the {RuNO} group. In both cases, the Ru − NO bond order sharply decreases 1 ; however, these transitions are symmetry forbidden or have a very low intensity, and the corresponding EES can be populated, first of all, through deactivation of states with higher energy. Therefore, the complex should contain an "antenna" fragment, which efficiently absorbs light in the visible or near-UV region. The calculations con-Abstract -The B3LYP method in the LanL2DZ basis set was used to carry out geometry optimization for the binuclear bridged complexes [ RuCl 4 3+ (Pyz is pyrazine). The electronic spectra of the complexes were calculated by the TDDFT and CINDO-CI methods with allowance for solvation effects. The ground-state electronic configurations of the two ruthenium atoms in these compounds were shown to be different. Among the lower excited states of all complexes, states with essentially weakened Ru-NO bonds were found. The strong absorption in the visible region of the spectrum of [ Ru ( Py ) 4 NO -CN -Ru ( Py ) 4 CN ] 3+ is due to the interfragment electron transfer Ru II {RuNO} accompanied by weakening of the bond between nitrogen oxide and the complex.