Investigation of the solvatochromic electronic transitions of [Ru(NH3)4bipyridine]2+

The electronic transitions of [Ru(NH3)4bipyridine]2+ were examined. The two longest wavelength absorption bands red-shift with increasing Gutmann donor number of the solvent, and the lowest energy band is split by about 1500 cm−1 in a mixed alcohol glass at 77 K. INDO/S calculations were employed to interpret the solvent-dependent electronic spectrum. The calculation predicts a number of closely spaced dπ → π∗ transitions, polarized in the plane of the bipyridine, as well as weak perpendicularly polarized non-bonding d→π∗ transitions. The results point out the limitations of simple molecular orbital descriptions of nominal metal-to-ligand charge-transfer transitions.