Flow microcalorimetry in stepwise equilibria of metal complexes. Reactions of NN′- and NN-diethylethylenediamine with hydrogen and copper(II) ions

Abstract

Enthalpy values associated with the stepwise reactions of hydrogen and copper(II) ions with the two isomeric diamines NN′- and NN-diethylethylenediamine have been determined by flow microcalorimetry at 25° C and I= 0·5M(NaClO₄). Combination with the reported ΔG^⊖ values gives appropriate ΔS^⊖ values. Comparison with the results for ethylenediamine shows that ethyl substitution causes a decrease in exothermicity of the reactions of protonation and complex formation and leads to a larger entropy change. In general, reactions with the symmetrical ligand are more exothermic than those of the asymmetrical one. The method of measuring and calculating enthalpies of stepwise reaction from flow-microcalorimetric data is described in detail.