The connection between the optical and thermodynamic characteristics of transition metal compounds

Abstract

The energy of stabilization of the crystal field (ESCF) for the MX₆ group may be calculated from thermodynamic and from optical data. Values of ESCF obtained from thermodynamic data are always greater than the corresponding values calculated from optical data. The reason for these deviations lies in the inaccuracy of the existing equation for evaluating ESCF from thermodynamic data. The two means arrived at for evaluating ESCF are in agreement with each other if a correction is introduced into the equation for the nonlinear character of the change in the ionic radii of the transition elements by using the “correlation radii” suggested in this paper. Correlation radii have been found for the bivalent ions of manganese, iron, cobalt, nickel, and copper. An equation has been proposed for evaluating the coulomb integrals and the effective charges on the metal atoms in MX₆ groups, based upon spectroscopic data (using the parameters D_q). The coulomb integrals and the effective charges on the metal atoms have been calculated in the complexes M(H₂O) ²⁺₆ (where M=Fe, Co, Ni), M (NH₃) ²⁺₆ (where M=Co, Ni), and NiF ⁴₆ . On the basis of these data the “effective bondings” characterizing the difference in the thermodynamic stability of the complexes considered have been calculated.