Metal-to-ligand charge-transfer excited-state photochemistry of [Cr(CO)5(C4H4N2)] and [Cr(CO)4(NC5H4CHNPri)]. The difference between the photochemical behaviour of [Cr(CO)5(C4H4N2)] in solution at 243 K and in an argon matrix at 10 K

Abstract

Irradiation of [Cr(CO)₄(NC₅H₄CHNPrⁱ)] in solution within the lowest Cr-to-di-imine charge-transfer band causes photosubstitution of a cis carbonyl ligand. Free CO and fac-[Cr(CO)₃(NC₅H₄CHNPrⁱ)] are formed when the complex is irradiated within this absorption band in matrices at 10 K. On the other hand, irradiation of a solution of [Cr(CO)₅(C₄H₄N₂)] within the Cr-to-pyridazine charge-transfer band mainly causes photosubstitution of pyridazine, whereas free CO and cis-[Cr(CO)₄(C₄H₄N₂)] are formed upon irradiation of this complex in a matrix. These results are discussed in relation to the lifetimes of the metal-to-ligand charge-transfer excited states and to the resonance-Raman spectra of these complexes.