The determination by a dilatometer technique of ion pairing constants and volume changes of ion pairing for [Co(en) 3] 3+ with Cl −, Br −, I −, NO 3−, ClO 4−, SO 42−, citrate and oxalate

Abstract

Dilatometry experiments are used to extract both the equilibrium constant K ip o and the volume change ;̄ ip for ion pairing. In a primary experiment the ion pairing anion (Cl −, Br −, I −, NO 3 −, SO 4 2−, C 2O 4 2− and C 6H 5O 7 3−) is injected into dilute [Co(en) 3](Clo 4) 3; in an auxiliary experiment the cobalt complex perchlorate is injected into the alkali metal anion solution at relatively high concentration. The latter experiment is dominated by the volume change on ion pairing whilst the primary experiment involves both parameters significantly, so an iterative analysis (with corrections for ion pairing of the perchlorate solution) allows joint extraction for the seven anions of K ip o and ;̄ ip at 298K. The K ip o of [Co(en) 3] 3+f and ClO 4 − at 278, 288, 308 and 318K was also determined by dilatometry.