Empirical relation between covalence and the energy position of the Ni2+1E state in octahedral complexes

In this paper, a simple empirical equation that relates the energy of the spin-forbidden 3A2-1E transition of the octahedrally coordinated Ni2+ ion with the recently introduced β1=(B/B0)2+(C/C0)2 parameter is derived (B, C (B0, C0) are the Racah parameters of Ni2+ ions in a crystal (free state), respectively). It is shown that the β1 parameter which simultaneously takes into account the reduction in both the Racah parameters B and C due to the nephelauxetic effect, is much more accurate in estimating the energy position of the Ni2+1E state than the commonly used nephelauxetic ratio β=B/B0, which completely ignores the reduction in the values of the Racah parameter C when the transition metal ion is introduced in the solid.