Thermodynamics of protonated amine-hexacyanoferrate(II) complex formation in aqueous solution

Thermodynamic parameters, Delta G degrees, Delta H degrees and T Delta S degrees are reported for the formation of proton amine-hexacyanoferrate(II) complexes, in aqueous solution, at 25 degrees C. Delta H degrees were determined by the temperature dependence of formation constants and/or by direct calorimetry in aqueous solution, at T = 25 degrees C. Enthalpy changes for the reaction H(j)A(i+) + HjFe(CN)(6)(j-4) = AFe(CN)(6)H-i+j(i+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 T Delta S degrees = 13.4 i kJ-mol(-1).