Systematic interpretation of experimentally measured and theoretically calculated spectra of transition-metal compounds by an optimized, linearized crystal field fitting procedure

Abstract

Linearized, least-squares fitting of experimental and theoretical spectra of transition-metal clusters by the crystal field (CF) model yields not only the usual systematically optimized CF orbital splitting and Racah parameters but also a convenient and direct measure of the sensitivity of the transition energies to those various quantities. Specifically considered are the transitions observed for Cr 3+ and Ni 2+ ions in octahedral fluoride clusters. The quality of the fit is less influenced by the Racah C B ratio than by the scaling of the metal d orbitals (i.e., the nephelauxetic effect). Consistent fittings of observed and SCF-MO-calculated spectra of NiF 6 4− and CrF 6 3− show very close agreement in values of, and sensitivities to, the CF parameter 10 Dq, the nephelauxetic factor, and the effective orbital population, the last being a direct measure of breakdown of the orbital approximation to the wavefunction. In comparing Racah parameters for free and complexed ions it is essential to choose values such that the same degree of electron correlation is encompassed in both cases.