Calculation of Crystal Field Splittings in Distorted Coordination Polyhedra: Spectra and Thermodynamic Properties of Minerals

Bernard J. Wood and R. G. J. Strens
Department of Geology, The University, Manchester M13 9PL, England
School of Physics, The University, Newcastle NE1 7RU, England

Summary: A simple method has been developed for calculating the d-orbital energy levels of transition-metal ions in coordination polyhedra with both orthogonal and non-orthogonal distortions, using equations based on those derived by Ballhausen (1954). The input data are atomic coordinates, a standard value of the crystal field splitting parameter Δ at known metal-ligand distance, and the ratio of radial integrals B2/B4, which is approximately constant for a given ion. The method can be applied to polyhedra containing different ligands.

Application of the equations to the Mn3+ (M3) site in piemontite and the Fe2+ (M2) site in orthopyroxene gives calculated transition energies in good agreement with the observed band energies.

The calculations permit definite assignment of the great majority of d-d absorption bands even in multi-site phases, and enable discrimination of crystal-field and charge-transfer bands in mineral spectra. They also throw light on the fine structures of both oxygen → metal and metal → metal charge-transfer bands, and allow the calculation of crystal-field stabilization enthalpy and electronic entropy. The latter is a previously neglected energy term that contributes significantly to the energetics of reactions within and between phases containing transition-metal ions.

Mineralogical Magazine; December 1972 v. 38; no. 300; p. 909-917; DOI: 10.1180/minmag.1972.038.300.01
© 1972, The Mineralogical Society
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