Thermodynamics of formation of lanthanide hydroxo complexes in aqueous solutions

Gibbs energies of formation have been determined by conductometric titration for hydroxo complexes of cerium, samarium, europium, erbium, ytterbium, and yttrium. All these elements form monohydroxo complexes; yttrium, erbium, and terbium also form dihydroxo complexes. The Gibbs energies of formation of lanthanide hydroxo complexes from ions have virtually equal values of -47.3 +/- 0.6 kJ/mol monohydroxo complexes and -44.5 +/- 0.5 kJ/mol for dihydroxo complexes, respectively. These values were used to estimate the Gibbs energies of formation of hydroxo complexes for the entire lanthanide series.