Thermodynamics of Protonated Amine–Hexacyanoferrate(II) Complex Formation in Aqueous Solution

Thermodynamic parameters, ΔG°, ΔH° and TΔS° are reported for the formation of proton amine–hexacyanoferrate(II) complexes, in aqueous solution, at 25°C. ΔH° were determined by the temperature dependence of formation constants and/ or by direct calorimetry in aqueous solution, at T = 25°C. Enthalpy changes for the reaction HiAi+ + Hj Fe(CN)6j-4 = AFe (CN)6Hi+ji+j-4 (where A = methylamine, ethylenediamine, and tetraethylenepentamine) are quite low and the main contribution to the stability of these complexes arises from the entropic term, as expected for electrostatic interactions. When j = 0, the formation entropy is linearly dependent on i according to the simple equation TΔS° = 13.4 i kJ-mol−1.