Inorganic Chemistry, Vol.34, No.24, 6215-6217, 1995
Resonance Raman-Spectroscopy of Ruthenium(II) and Osmium(II) Polypyridyl Complexes Containing the N-Methyl-4,4’-Bipyridinium Radical (Mq(Center-Dot)) as a Ligand - Evidence for a M(D-Pi)-)Mq(Center-Dot)(Pi-Asterisk) Metal-to-Ligand Charge-Transfer (MLCT) Transition
Free N-methyl-4,4’-bipyridinium radical (MQ(.)) displays broad, visible absorptions at 360 and 600 nm that can be assigned to pi --> pi* and pi* --> pi* (MQ(.)) transitions. Excitation-dependent resonance Raman measurements on MQ(.), [(bpy)(2)Ru(MQ(.))(2)](2+), and [(bpy)(2)Os(CO)(MQ(.))](2+) indicate that new absorption bands in the complexes are MQ(.)-based and causes significant resonance enhancements for modes affected by a change in the oxidation state at the metal. The new band is assigned to a MII --> (d pi) -->MQ(.)(pi*) metal-to-ligand charge transfer (MLCT) transition.