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 (H 2 bihyat) for [U VI O 2 ] 2+ , novel binucleating ligands (BLs) N , N ', N ″, N‴ -((1,4-phenylenebis(oxy))bis(1,3,5-triazine-6,2,4-triyl))tetrakis( N -methylhydroxylamine) (H 4 qtn), N 1 , N 4 -bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)benzene-1,4-diamine (H 4 pdl), and N 1 , N 2 -bis(4,6-bis(hydroxy(methyl)amino)-1,3,5-triazin-2-yl)ethane-1,2-diamine (H 4 enl) were synthesized. Binuclear complexes formed by coordination of hard metal ions with H 4 qtn are thermodynamically more stable than their mononuclear analogues with H 2 bihyat due to the increase in entropy accompanying the formation of more chelate rings. Reaction of either H 4 qtn or H 4 pdl or H 4 enl with [U VI O 2 ] 2+ and [V V O 2 ] + resulted in the isolation of the binuclear complexes [(U VI O 2 ) 2 (μ-qtn)(H 2 O) 4 ] ( 1 ), [(V V O 2 ) 2 (μ-qtn)][PPh 4 ] 2 [PPh4] ( 2 ), [(U VI O 2 ) 2 (μ-pdl)(H 2 O) 2 (MeOH) 2 ] ( 3 ), [(V V O 2 ) 2 (μ-pdl)][PPh 4 ] 2 ( 4 ), [(U VI O 2 ) 2 (μ-enl)(H 2 O) 4 ] ( 5 ), and [(V V O 2 ) 2 (μ-enl)][PPh 4 ] 2 ( 6 ). The binuclear complexes 1-6 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 (H 2 dipic) or H 2 bihyat or CO 3 2- toward [U VI O 2 ] 2+ and [V V O 2 ] + was investigated by NMR and UV-vis spectroscopies and DFT theoretical calculations, revealing a superior performance of BLs. The selectivity of the BLs for [U VI O 2 ] 2+ over [V V O 2 ] + is decreased compared to that of H 2 bihyat but increases considerably at pH > 9 values. Formation of the mixed-metal binuclear species [U VI O 2 (μ-O)V V O 2 ] influences the selectivity and dynamics of the reaction of H 4 qtn for [U VI O 2 ] 2+ and [V V O 2 ] + in aqueous solution. The results of this study provide crucial information for the ligand design and the development of stronger and more selective systems.