Ligand field analysis of Mn5+ in tetra-oxo coordination

Abstract

Abstract Polarized single crystal absorption and powder reflection spectra of Mn5+ (d2) in tetrahedral oxo-coordination of host compounds with the spodiosite and apatite structure from literature are analysed using the angular overlap model (AOM). A small number of model parameters such as the AOM parameters eσ and eπ, the interelectronic repulsion parameters B and C as well as geometric distortion angles 2θ were used to fit the band positions. Covalency is pronounced, however, enforcing a treatment with varying B values for different strong field configurations e2, e1t21, t22− the C/B ratios being kept at the free ion value of 4.25. Deduced best-fit parameter values are Δ ≈ 10650 cm−1 (eσ ≈ 12000 cm−1, eσ/eπ = 4), Bee ≈ 530 cm−1, Bet ≈ 420 cm−1, Btt ≈ 340 cm−1, showing that the central field covalency dominates over the symmetry restricted covalency. The estimated angular distortion parameters 2θ and the Δ values indicate that the geometry of the tetrahedral sites is significantly modified when Mn5+ is incorporated into positions of host ions with a smaller ionic radius (P5++).