Bis(hydroxylamino)triazines: High Selectivity and Hydrolytic Stability of Hydroxylamine-Based Ligands for Uranyl Compared to Vanadium(V) and Iron(III).

The development of ligands with high selectivity and affinity for uranium is critical in the extraction of uranium from human body, radioactive waste, and seawater. A scientific challenge is the improvement of the selectivity of chelators for uranium over other heavy metals, including iron and vanadium. Flat ligands with hard donor atoms that satisfy the geometric and electronic requirements of the UO exhibit high selectivity for the uranyl moiety. The bis(hydroxylamino)(triazine) ligand, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (Hbihyat), a strong binder for hard metal ions (Fe, Ti, V, and Mo), reacted with [UO(NO)(HO)]·4HO in aqueous solution and resulted in the isolation of the complexes [UO(bihyat)(HO)], [UO(bihyat)], and {[UO(bihyat)(μ-OH)]}. These three species are in equilibrium in aqueous solution, and their abundance varies with the concentration of Hbihyat and the pH. Reaction of Hbihyat with [UO(NO)(HO)]·4HO in CHCN gave the trinuclear complex [UO(bihyat)(μ-bihyat)], which is the major species in organic solvents. The dynamics between the UO and the free ligand Hbihyat in aqueous and dimethyl sulfoxide solutions; the metal binding ability of the Hbihyat over pyridine-2,6-dicarboxylic acid (Hdipic) or glutarimidedioxime for UO, and the selectivity of the Hbihyat to bind UO in comparison to VO and Fe in either UO/VO or UO/Fe solutions were examined by NMR and UV-vis spectroscopies. The results revealed that Hbihyat is a superior ligand for UO with high selectivity compared to Fe and VO, which increases at higher pHs. Thus, this type of ligand might find applications in the extraction of uranium from the sea and its removal from the environment and the human body.