Formation of five-co-ordinate cations between copper(II) polyamine complexes and some inorganic anions. Standard thermodynamic functions in methanol at 25 °C

Abstract

The standard thermodynamic functions for the equilibrium [CuL]²⁺+ X-⇌[CuLX]⁺ with L = 2 en, 2 tn, trien, (2,3,2-tet), and (3,3,3-tet)[i.e., ethylenediamine, trimethylenediamine, triethylenetetramine, NN′-bis(2-aminoethyl)propane-1,3-diamine, and NN′-bis(3-aminopropyl)propane-1,3-diamine respectively] and X^–= iodide, thiocyanate, and azide ions have been studied in methanol at 25 °C. The equilibrium constants have been measured by a spectrophotometric method. The heats of reaction have been determined directly by calorimetric titration. The enthalpies of formation are all positive or only slightly negative, while the entropies are largely positive. For each copper(II) polyamine complex the enthalpy and entropy changes decrease in the order: N₃^– > I^– > SCN^–. In the reactions with the same inorganic anion ΔH° and ΔS° decrease according to the sequence [Cu(en)₂]²⁺ > [Cu(trien)]²⁺≃[Cu(2,3,2-tet)]²⁺ > [Cu(tn)₂]²⁺ > [Cu(3,3,3-tet)]²⁺.