First and second association constants of unsymmetrical metal-chelate electrolytes from conductance measurements. Tris(1,10-phenanthroline)iron(II) perchlorate in nitrobenzene + carbon tetrachloride mixtures at 25 °C

Abstract

The conductances of tris(1,10-phenanthroline)iron(II) perchlorate {[Fe(phen)₃](ClO₄)₂} have been measured in nitrobenzene + carbon tetrachloride mixtures covering the approximate range of dielectric constant 36–16 at 25 °C. The metal-chelate electrolyte was found to be so associated in mixtures with a dielectric constant < ca. 21 that secondary association cannot be disregarded. To estimate the second ionic association constant the Jenkins–Monk method was extended; the degree of first and second association is estimated by introducing the ratio of first and second association constants K_a1/K_a2, which is calculated as a function of the ionic distance parameter using the Fuoss equation of ionic association, and an iterative calculation to obtain the best K_a1 and K_a2 values was carried so that the concentration dependence of the first association constant is minimal. A plot of log K_a2 against 1/ε shows a curve concave downwards and the K_a2 values for ε < 18 are comparable to those of (i-Pent)₃BuNBPh₄.