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), 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 mum(-1) (I mum(-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 mum(-1) for the M(V) ions. The intense bands above 3.6 mum(-1) for M(IV) and 4.6 mum(-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 pi * orbitals. The prominent intense bands observed below 4.5 mum(-1) for the M(V) complexes are assigned as ligand to metal charge transfer (LMCT) from occupied non-bonding or weakly pi bonding CN- orbitals to the half-filled b(1)(x(2)-y(2)) HOMO. (C) 2003 Elsevier B.V. All rights reserved.