Enthalpic control of zinc-water acidity in complexes of tris(2-aminoethyl)amine and tris(2-dimethylaminoethyl)amine

The enthalpies of ionization of zinc-bound water in the complexes (ZntrenOH2)2+ and (ZnMe6trenOH2)2+ are determined by titration calorimetry and potentiometric methods. The difference in the zinc-water acidity is due to enthalpic effects. High acidity of the complex (ZnMe6trenOH2)2+ compared to (ZntrenOH2)2+ is due to the low inonization enthalpy of the former. The observed enthalpic control denotes the ability of coordination complex to stabilize charge.