Lattice Potential Energy Estimation for Complex Ionic Salts from Density Measurements

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Abstract
This paper is one of a series exploring simple approaches for the estimation of lattice energy of ionic materials, avoiding elaborate computation. The readily accessible, frequently reported, and easily measurable (requiring only small quantities of inorganic material) property of density, ρm, is related, as a rectilinear function of the form (ρm/Mm)1/3, to the lattice energy UPOT of ionic materials, where Mm is the chemical formula mass. Dependence on the cube root is particularly advantageous because this considerably lowers the effects of any experimental errors in the density measurement used. The relationship that is developed arises from the dependence (previously reported in Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J.; Glasser, L. Inorg. Chem. 1999, 38, 3609) of lattice energy on the inverse cube root of the molar volume. These latest equations have the form UPOT/kJ mol-1 = γ(ρm/Mm)1/3 + δ, where for the simpler salts (i.e., UPOT/kJ mol-1 < 5000 kJ mol-1), γ and δ are coefficients dependent upon the stoichiometry of the inorganic material, and for materials for which UPOT/kJ mol-1 > 5000, γ/kJ mol-1 cm = 10-7AI(2INA)1/3 and δ/kJ mol-1 = 0 where A is the general electrostatic conversion factor (A = 121.4 kJ mol-1), I is the ionic strength = ∑nizi2, and NA is Avogadro's constant.