LIGAND-FIELD ANALYSIS OF MN5-OXO COORDINATION( IN TETRA)

Polarized single crystal absorption and powder reflection spectra of M n5+ (d(2)) in tetrahedral ore-coordination of host compounds with the spodiosite and apatite structure from literature are analysed using th e angular overlap model (AOM). A small number of model parameters such as the AOM parameters e sigma and e pi, the interelectronic repulsion parameters B and C as well as geometric distortion angles 2 theta wer e used to fit the band positions. Covalency is pronounced, however, en forcing a treatment with varying B values for different strong field c onfigurations e(2), e(1)t(2)(1), t(2)(2) - the C/B ratios being kept a t the free ion value of 4.25. Deduced best-fit parameter values are De lta approximate to 10650 cm(-1) (e sigma approximate to 12000 cm(-1), e sigma/e pi = 4), B-ee approximate to 530 cm(-1), B-et approximate to 420 cm(-1), B-tt approximate to 340 cm(-1), showing that the central field covalency dominates over the symmetry restricted covalency. The estimated angular distortion parameters 2 theta and the Delta values i ndicate that the geometry of the tetrahedral sites is significantly mo dified when Mn5+ is incorporated into positions of host ions with a sm aller ionic radius (P5+).