Uranyl ion complexes with aminoalcoholbis(phenolate) [O,N,O,O′] donor ligands

The reaction between uranyl nitrate hexahydrate and phenolic ligand precursor N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-2-aminoethanol (H3L1) in acetonitrile without base affords the dinuclear uranyl complex [(UO2)2(H2L1)2(NO3)2] (1); in the presence of base, the mononuclear complex [UO2(H2L1)2] · 2H2O (2) is formed. Ligand N,N-bis(2-hydroxy-5-t-butyl-3-methylbenzyl)-2-aminoethanol (H3L2) affords a uranyl complex of formula [UO2(H2L2)2] · 2CH3CN (3); ligand N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-3-amino-1-propanol (H3L3) affords a uranyl complex of formula [UO2(H2L3)2] (4); whilst ligand N,N-bis(2-hydroxy-5-t-butyl-3-methylbenzyl)-3-amino-1-propanol (H3L4), used as the hydrochloride, affords a uranyl complex of formula [UO2(H2L4)2] (5). A solid complex with uranyl ion could not be formed using the ligand N,N-bis(2-hydroxy-3,5-di-t-butylbenzyl)-2-aminoethanol. The molecular structures of 1–5 were verified by X-ray crystallography whereby it was ascertained that 1 is a dialkoxo-bridged dinuclear uranyl complex with a U to L ratio of 1:1. The other complexes 2–5 form in a molar ratio of 1:2 (U to L) 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.

Graphical abstractThe reaction between uranyl nitrate hexahydrate and phenolic ligand precursor N,N-bis(2-hydroxy-3,5-dimethylbenzyl)-2-aminoethanol (H3L1) in acetonitrile without base affords the dinuclear uranyl complex [(UO2)2(H2L1)2(NO3)2] (1); in the presence of base, the mononuclear complex [UO2(H2L1)2] · 2H2O (2) is formed. Ligands (H3L2–H3L4), similar to H3L1, formed only the complexes of the type 2. Extraction studies of the uranyl ion from water to dichloromethane with these ligands are also presented.Figure optionsDownload full-size imageDownload as PowerPoint slide