Absorption Spectra of Tetrahedral Co(III) and Co(II) Complexes in Heteropolytungstates

Abstract The absorption spectra of Co(III) and Co(II) in the single crystals of the Keggin-structure compounds, K5CoIIIW12O40·nH2O and K6CoIIW12O40·mH2O, have been measured at 77 K. The spectra of these complexes in aqueous solutions have also been observed. All the spectra have been interpreted using crystal-field theory by assuming that a Co(III) or Co(II) ion is in Td symmetry. The parameters, Dq, B, and C⁄B can be evaluated as 780 cm−1, 630 cm−1, and 4.7 respectively for the Co(III) complex, and 460 cm−1, 650 cm−1, and 4.5 respectively for the Co(II) complex.