Heteropolytungstate complexes of the lanthanide elements. Part II. Electronic spectra: a metal–ligand charge-transfer transition of cerium(III)

The small nephelauxetic parameters dβ for lanthanide heteropolytungstate complexes show that the Ln–O bond is essentially ionic. The absorption spectra of the EuIII complexes indicate, in each case, site symmetry not higher than tetragonal for the lanthanide; the emission spectra of EuW10O357– and Eu(SiW11O39)211– in the solid state agree best with D2d and D4h microsymmetry respectively. The bands causing the brown colours of the CeIII complexes, whose wavenumbers increase with the CeIV/CeIII redox potential, are assigned to metal–ligand charge-transfer.