Knowledge Bank

The electronic spectra of Ru(II) complexes with organic ligands generally exhibit strong absorptions attributable to metal-to-ligand charge transfer $(MLCT).1$ MLCT can be viewed as a redox process in which an electronically excited state composed of an oxidized metal ion and an organic radical anion is formed. The energy of the MLCT state in relation to the lowest $d-d\ast$ ligand-field (LF) transition is quite sensitive to the nature of the organic ligand, including its $substituents.2$ We have investigated both ground and low-lying excited electronic states of a series of ruthenium (II) pentaammine pyridine derivatives, $Ru(NH3)$ [FIGURE] where R = acetyl, benzoyl, etc. by resonance Raman spectroscopy. The complexes were irradiated with either cw or pulsed laser radiation; in the latter case the same laser pulse was utilized to both prepare and probe the excited electronic state. The ligand Raman spectra in the ground and MLCT states differ significantly. The results will be compared to Raman spectra of the ground state ligand anions, and the excited electronic state assignments will be correlated with the extensive photochemical literature.