Superposition model analysis from polarized electronic absorption spectra of Co2+ in trigonally distorted octahedra in brucite-type Co(OH)2

Polarized electronic absorption spectra of Co2+ in trigonally compressed octahedra in brucite-type Co(OH)2 have been measured at 290 and 90 K by microscope-spectrometric techniques and analysed in terms of the superposition model (SM) of crystal fields. The resulting SM and interelectronic repulsion parameters are B-bar4=5260, B-bar2=4920, Racah B = 825, Racah C = 3550 cm-1 at 290 K and B-bar4=5320, B-bar2=3900, Racah B = 830, Racah C = 3500 cm-1 at 90 K (R0 = 2.1115 A; fixed exponential and spin-orbit parameters t4=5, t2=3, ζ = 500 cm-1). Together with a recent SM analysis of Li2Co3(SeO3)4, the B-bark refined for Co(OH)2 further confine the magnitude of the hitherto unknown 'correct' SM parameters of Co2+ for future application to structurally and/or chemically less well defined systems. (author)