Investigation of MLCT and ML′CT transitions of M(CO) 3LL′ complexes, (M = Cr, Mo, W; L = diimine; L′ = isocyanide) with the resonance raman effect. Identification of two isomers of the p-nitrophenylisocyanide complex

Abstract

The resonance Raman (RR) spectra of the complexes M(CO) 3LL′ (M = Cr, Mo, W; L = N,N′-di(i-propyl)-1,4-diazubutadiene, pyridine-2-carbaldehyde-(i-propyl)imine; L′ = CNR with R = t-butyl, p-CH 3-phenyl, p-Cl-phenyl and p-NO 2-phenyl) have been investigated by exciting within the metal-to-ligand L and L′ transitions. With the use of these RR spectra the CT transitions to these ligands L and L′ could be characterized. The properties of the excited electronic states of these complexes are discussed and related to those of the corresponding complexes containing L′ = P(OMe) 3 and CO. In the case of L′ = p-nitrophenylisocyanide two (CN) stretching modes are observed in the infrared and Raman spectra. Their origin and the change of relative intensity in the RR spectra is discussed. Irradiation within the MLCT as well as the ML′CT band causes photosubstitution of the carbonyl ligand cis with respect to the diimine with quantum yields varying from 10 −3 to 10 −5. The relationship between the photoreactivity and RR behaviour is discussed.