Electronic absorption and MCD spectra for octacyanometallate complexes M(CN) 8 n− , M=Mo(IV), W(IV), n=4 and Mo(V), W(V), n=3

Abstract

Electronic absorption and 8.0 T magnetic circular dichroism (MCD) spectra are reported for M(CN) 8 4− , M=Mo(IV) and W(IV), in aqueous solution and M(CN) 8 3− , M=Mo(V) and W(V), in acetonitrile solutions. In addition some absorption and MCD spectra are reported for the M(CN) 8 3− ions embedded in thin poly methyl methacrylate (PMMA) plastic films at temperatures from 295 to 10 K. The temperature dependence of the MCD spectra confirms the presence of C terms. The solution and PMMA spectra for the both Mo and W complexes in either the IV or V oxidation states are remarkably similar to each other for the same oxidation state and are interpreted within a D 2d structural framework for the isotropic environment. The weak bands below 3.0 μm −1 (1 μm −1=10 4 cm −1) for the M(IV) complexes are assigned as metal-localized ligand field (LF) transitions. LF transitions are also suggested for weaker unresolved absorption between 3.0 and 3.6 μm −1 for the M(V) ions. The intense bands above 3.6 μm −1 for M(IV) and 4.6 μm −1 for M(V) complexes are interpreted as metal to ligand charge transfer (MLCT) from the metal b 1( x 2− y 2) HOMO to CN −-based π * orbitals. The prominent intense bands observed below 4.5 μm −1for the M(V) complexes are assigned as ligand to metal charge transfer (LMCT) from occupied non-bonding or weakly π bonding CN − orbitals to the half-filled b 1( x 2− y 2) HOMO.