Thermodynamics of nickel(II) and iron(III) complexation with nicotinamide in aqueous ethanol and aqueous dimethyl sulfoxide

Highlights: • The enthalpy changes of Ni²⁺ and Fe³⁺ with nicotinamide in aqueous organic solvents are determined. • The reagents with dominant contribution in the thermodynamic characteristics of reaction transfer are established. • The solvation of Ni²⁺ ions and its complexes with nicotinamide is studied. • No contact ion pairing between Ni²⁺ and ClO₄^- is observed. - Abstract: The complexation of Ni(II) and Fe(III) with nicotinamide in aqueous ethanol and aqueous dimethyl sulfoxide was directly studied by calorimetry at T = 298.15 K and ionic strength value 0.25 (NaClO₄). The results of thermochemical study were discussed using solvation-thermodynamic approach basing on the accounting of reagents solvation. The absence of contact ion pairing between Ni²⁺ and ClO₄^- was observed by IR-spectroscopy at ionic strength value 0.25. Nicotinamide was found to replace the water molecule within cation coordination sphere by means of UV–Vis spectroscopy