FORMATION CONSTANTS OF SOME RARE-EARTH COMPLEXES

The stepwise formation constants for complexes between the trivalent metals lanthanum, yttrium, and all of the rare earths, except promethium, and the ligands isobutyrate (IBU), alpha -hydroxyisobutyrate (AHIB) and alpha , BETA , BETA '-trihydroxyisobutyrate (THIB) were measured at 25 deg C and an ionic strength of 0.5M (NaClO/sub 4/). For lanthanum and the first half of the rare- earth series, the magnitude of the formation constants increased in the order IBU, AHIB, THIB. For the remainder of the series and yttrium, the magnitude increased in the order IBU, THIB, AHIB. It was postulated that the inversion of the AHIB and THLB stabilities with increasing atomic number was brought about by a change in the number of coordination sites of the metal which could be occupied by the THIB ligand. The IBU and THIB complex formation constants both exhibit a sinusoidal behavior when plotted as a function of atomic number. Such a plot for the AHIB complexes increases more or less uniformly. Because of this, it was concluded that the AHIB would be the superior ligand to use as an eluant for ion- exchange chromatographic separation of rare-earth mixtures. (auth