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-hexacyanofer rate(II) complexes, in aqueous solution, at 25 degrees C. Delta H degr ees were determined by the temperature dependence of formation constan ts 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) = A Fe(CN)(6)H-i+j(i+j-4) (where A = methylamine, ethylenediamine, and tet raethylenepentamine) are quite low and the main contribution to the st ability of these complexes arises from the entropic term, as expected for electrostatic interactions. When j = 0, the formation entropy is l inearly dependent on i according to the simple equation T Delta S degr ees = 13.4 i kJ-mol(-1).