Design and Modulation of Selectivity toward Vanadium(V) and Uranium(VI) Ions: Coordination Properties and Affinity of Hydroxylamino-Triazine Siderophores.

Based on the strong binding and high selectivity properties of 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (Hbihyat) for [UO], novel binucleating ligands (BLs) ,',″,-((1,4-phenylenebis(oxy))bis(1,3,5-triazine-6,2,4-triyl))tetrakis(-methylhydroxylamine) (Hqtn), ,-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)benzene-1,4-diamine (Hpdl), and ,-bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)ethane-1,2-diamine (Henl) were synthesized. Binuclear complexes formed by coordination of hard metal ions with Hqtn are thermodynamically more stable than their mononuclear analogues with Hbihyat due to the increase in entropy accompanying the formation of more chelate rings. Reaction of either Hqtn or Hpdl or Henl with [UO] and [VO] resulted in the isolation of the binuclear complexes [(UO)(μ-qtn)(HO)] (), [(VO)(μ-qtn)][PPh][PPh4] (), [(UO)(μ-pdl)(HO)(MeOH)] (), [(VO)(μ-pdl)][PPh] (), [(UO)(μ-enl)(HO)] (), and [(VO)(μ-enl)][PPh] (). The binuclear complexes were characterized by single-crystal X-ray diffraction analysis in solid state and by NMR and ESI-MS in solution. The comparison of the coordination ability of the BLs with either pyridine-2,6-dicarboxylic acid (Hdipic) or Hbihyat or CO toward [UO] and [VO] was investigated by NMR and UV-vis spectroscopies and DFT theoretical calculations, revealing a superior performance of BLs. The selectivity of the BLs for [UO] over [VO] is decreased compared to that of Hbihyat but increases considerably at pH > 9 values. Formation of the mixed-metal binuclear species [UO(μ-O)VO] influences the selectivity and dynamics of the reaction of Hqtn for [UO] and [VO] in aqueous solution. The results of this study provide crucial information for the ligand design and the development of stronger and more selective systems.