Density functional theory calculations of selected Ru(II) two ring diimine complex dications

Geometry optimization for a series of ten, two-ring diimine Ru(II) complexes was effected using the Gaussian 98 protocol at density functional theory (DFT) B3LYP level with basis sets 3-21G((*)) and 3-21G((*)(*)). HOMO-LUMO energy difference values compared favorably to the experimental data from electrochemistry [DeltaE(1/2) = (E-1/2ox - E-1/2red)] and the lowest energy absorption maxima, which for these complexes correspond to the metal-to-ligand charge transfer (MLCT) band, The HOMO and LUMO distributions from DFT support the idea that the lowest energy transitions are metal-to-ligand charge transfer and that the lowest energy LUMO for the mixed ligand complexes is located on 2,2'-bipyrazine (bpz), followed by 2,2'-bipyrimidine (bpm) and then 2,2'-bipyridine (bpy).