Thermochemical properties of Ln(Gly)4Im(ClO4)3·nH2O (Ln = Gd, Tb, Dy, Y)

The enthalpies of dissolution in water of new ternary complexes of four late trivalent lanthanide ions Ln(Gly)4Im(ClO4)3·nH2O (Ln=Gd, Tb, Dy, Y; Gly: glycine; Im: imidazole and n=1 or 2) were measured by means of a Calvet microcalorimeter. Empirical formulae for the calculation of the enthalpies of dissolution (ΔdissH), relative apparent molar enthalpies (ΔdissH (app)), relative partial molar enthalpies (ΔdissH (partial)) and enthalpies of dilution (ΔdilH1,2) were obtained from the experimental data of the enthalpies of dissolution of these complexes. The plot of ΔdissHmΘ, ΔdissH (app) and ΔdissH (partial) versus the values of the ionic radius of the lanthanide element (r) showed a grouping effect of the lanthanide elements, indicating that the coordinated bond between the lanthanide ions and the ligands has some covalent character. The unknown value of the standard enthalpy of dissolution for the similar complex: Ho(Gly)4Im(ClO4)3·H2O was estimated according to the plot of ΔdissHmΘ versus r.