Influence of the halogen ligand on the near-UV-visible spectrum of [Ru(X)(Me)(CO)2(alpha-diimine)] (X = Cl, l; alpha-diimine = Me-DAB, iPr-DAB; DAB = 1,4-Diaza-1,3-butadiene): An ab initio and TD-DFT analysis

CASSCF/CASPT2 and TD-DFT calculations are used to investigate the near-UV-vis electronic spectroscopy of [Ru(X)(Me)(CO)2(iPr-DAB)] (X = Cl or i; iPr-DAB = N,N'-di-isopropyl-1,4-diaza-1,3-butadiene. Both the methods reproduce the red shift of the absorption bands on going from the chloride to the iodide complex as well as the sift of the strongly absorbed higher MLCT (metal-to-ligand charge-transfer) transition from the visible to the UV domain of energy.