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

The electronic transitions of [Ru(NH3)(4)bipyridine](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 1 500 cm(-1) in a mixed alcohol glass at 77 K. INDO/S calculations were emplo yed to interpret the solvent-dependent electronic spectrum. The calculation predicts a number of closely spaced d(pi) --> pi* transitions, polarized i n the plane of the bipyridine, as well as weak perpendicularly polarized no n-bonding d --> pi* transitions. The results point out the limitations of s imple molecular orbital descriptions of nominal metal-to-ligand charge-tran sfer transitions. (C) 1999 Elsevier Science B.V. All rights reserved.