Aminoalkylbis(phenolate) [O,N,O] donor ligands for uranyl(VI) ion coordination: Syntheses, structures, and extraction studies

The syntheses of five new aminoalkylbis(phenolate) ligands (as hydrochlorides) and their uranyl complexes are described. The reaction between uranyl nitrate hexahydrate and phenolic ligand [(N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-1-aminopropane) · HCl], H2L1 · HCl, forms a uranyl complex [UO2(HL1)2] · 2CH3CN (1). The ligand [(N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-1-aminobutane) · HCl], H2L2 · HCl, forms a uranyl complex with a formula [UO2(HL2)2] · 2CH3CN (2). The ligand [(N,N-bis(2-hydroxy-5-tert-butyl-3-methyl benzyl)-1-aminohexane) · HCl], H2L3 · HCl, yields a uranyl complex with a formula [UO2(HL3)2] · 2CH3CN (3) and the ligand [(N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-cyclohexylamine) · HCl], H2L4 · HCl, yields a uranyl complex with a formula [UO2(HL4)2] (4). The ligand [(N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-benzylamine) · HCl], H2L5 · HCl, forms a uranyl complex with a formula [UO2(HL5)2] · 2MeOH (5). The molecular structures of 1, 2′ (2 without methanol), 3, 4 and 5 were verified by X-ray crystallography. The complexes 1–5 are neutral zwitterions which form in a molar ratio of 1:2 (U to L) in the presence of a base (triethylamine) and bear similar mononuclear, distorted octahedral uranyl structures with the four coordinating phenoxo ligands forming an equatorial plane and resulting in a centrosymmetric structure for the uranyl ion. In uranyl ion extraction studies from water to dichloromethane with ligands H2L1 · HCl–H2L5 · HCl, the ligands H2L2 · HCl and H2L4 · HCl are the most effective ones.

Graphical abstractThe syntheses of five new aminoalkylbis(phenolate) ligands (as hydrochlorides) and their uranyl complexes are described. The reaction between uranyl nitrate hexahydrate and phenolic ligand precursor [(N,N-bis(2-hydroxy-5-tert-butyl-3-methylbenzyl)-aminoalkyl) · HCl], (alkyl = propyl, butyl, hexyl, cyclohexyl or benzyl) (H2L1–H2L5), in acetonitrile in presence of a base affords the mononuclear, neutral complexes [UO2(HL)2] · xS (x = 0, 1 or 2 and S = acetonitrile or methanol). Extraction studies of the uranyl ion from water to dichloromethane with these new ligands (H2L1–H2L5) are also presented and the ligands H2L2 · HCl and H2L4 · HCl are the most effective ones.Figure optionsDownload full-size imageDownload as PowerPoint slide