Thermodynamics of the Formation of Mixed Complexes of Nickel(II) Ions with Histidine and Diamines in an Aqueous Solution

Calorimetry, spectrophotometry, and pH measurements are used to study the formation of mixed ligand complexes with 1,10-phenanthroline (Phen) and ethylenediamine (En) in Ni(II)–His–Phen(En) systems. The formation of mixed complexes with different stoichiometries is found, and the thermodynamic parameters ( log K , Δ r G 0 , Δ r H , Δ r S ) of the reactions of their formation at 298.15 K and ionic strength I = 0.5 (KNO 3 ) are calculated. The most likely form of the coordination of the amino acid residue in the composition of the mixed complexes is identified.