Spectrophotometric and conductometric study of complexation of salophen and some transition metal ions in nonaqueous polar solvents

The complexation reaction between Cu2+, Co2+ and Ni2+ metal cations with N,N′-bis(salicylidene)-1,2-phenylenediamine (salophen), in three nonaqueous polar solvents such as: acetonitrile (AN), dimethyl sulfoxide (DMSO), methanol (MeOH) and two binary mixtures of AN:DMSO and AN:MeOH at 25 °C were studied by spectrophotometric and conductometric methods. All investigated metal ions form 1:1 ML complex which their stability constants were determined and increase as Irving–Williams stability order of Co2+ < Ni2+ < Cu2+ in all solvent systems except in the pure MeOH and binary mixture of AN:MeOH 20:80; in which, Ni2+ < Co2+ < Cu2+ was observed. The values of the thermodynamic parameters (ΔH°, ΔS° and ΔG°) for complexation reactions obtained from the temperature dependence of the stability constants and the results show that for all metal ion complexes, the value of ΔH°, ΔS° and ΔG° are solvent dependent.