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

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 D2d structural framework for the isotropic environment. The weak bands below 3.0 μm−1 (1 μm−1=104 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 b1(x2−y2) 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 b1(x2−y2) HOMO.