Relative stabilities of dipositive and tripositive lanthanoid ions in aqueous solution

Values of E°[M3+/M2+] for the lanthanoid elements are estimated by using a simple ionic model and auxiliary thermodynamic data. The results correlate closely with the ionization potentials of the M2+ ions and are in good agreement with both chemical observations and other estimates obtained by spectroscopic correlations. This suggests that the method used here provides a quite general way of estimating thermodynamic data for those divalent lanthanoid compounds to which ionic models are commonly applied. Values of E°[M3+/M], calculated from recent thermodynamic data, are also tabulated.