Ground- and excited-state infrared spectra of an azacrown-substituted [(bpy)Re(CO)L-3](+) complex: Structure and bonding in ground and excited states and effects of Ba2+ binding

摘要

Ground- and excited-state infrared spectra are reported for a [(bpy)Re-I(CO)(3)L](+) complex (bpy = 2,2'-bipyridine) in which L contains an azacrown ether that is linked to Re via an amidopyridyl group. Ground-state band assignments are made with the aid of spectra from model complexes in which a similar electron-donating dimethylamino group replaces the azacrown, in which an electron-donor group is absent, and from the L ligands, in conjunction with DFT calculations. Picosecond time-resolved IR (TRIR) spectra in the v(CO) region show bands characteristic of a metal-to-ligand charge-transfer (MLCT) excited state, [(bpy(center dot-))Re-II(CO)(3)L](+), from the complex in which an electron-donor group is absent, whereas those from the azacrown complex show bands of an MLCT state evolving into those characteristic of a ligand-to-ligand charge-transfer (LLCT) excited state, [(bpy(center dot-))Re-I(CO)(3)(L center dot+)(+), formed upon intramolecular electron transfer. Picosecond TRIR spectra of the azacrown complex in the fingerprint region show strong L ligand bands that indicate that significant charge redistribution occurs within this ligand in the MLCT state and that decay as the LLCT state forms. Picosecond TRIR spectra obtained when Ball was complexed to the azacrown show bands of only an MLCT state at all times up to 2 ns, consistent with the presence of Ba2+ inhibiting electron transfer from the azacrown N atom to form the LLCT state, and the positions of the bands in the fingerprint region provide direct evidence for the proposal that charge redistribution within the L ligand induces Ba2+ release from the azacrown in the MLCT state.