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

•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.

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.

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