Role of the crystal field stabilization energy in the formation of metal(II) formate mixed crystals

Abstract

A relationship between the distribution coefficient values and the factors determining the isomorphous substitution of some metal(II) formates (Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd) has been found, given by D 2 / 1 = [ M 1.0 M 2.0 ] 2 exp ⁡ a ⋅ f [ Δ R R ] + b ⋅ ϕ ( Δ e ) + c ⋅ ψ ( Δ s ) R T , where Δ R/R is the relative difference in the ionic radii of the intersubstituting ions, Δɛ is the difference in the Me O bond energy, Δ s is the difference in the crystal field stabilization energy. The pre-exponential term represents the balance in bonding factors between the ions in the crystal and in the aqueous solution, in the case of ideally mixing in the solid state. The exponential term takes into account the enthalpy of mixing in the solid state. For the isostructural formate salts in which the substitution of a given cation by another one occurs in equivalent octahedral positions, the difference in the crystal field stabilization energy exerts the most important influence on the enthalpy of mixing.