Hydroxy- and alkoxy-bridged dinuclear uranyl–Schiff base complexes: hydrolysis, transamination and extraction studies

Abstract

The reaction of uranyl nitrate with 1,3-bis(salicylideneamino)-2-propanol (H(3)L1) and 1,3-bis(3,5-di-tert-butylsalicylideneamino)-2-propanol (H(3)L2) in the presence of triethylamine (Et(3)N) yielded hydroxy- and alkoxy-bridged dinuclear complexes; [(UO(2))(2)(L1)(OH)(MeOH)(2)].(MeOH)(2) (.(MeOH)(2)) and [(UO(2))(2)(L2)(OH)(MeOH)(2)].(MeOH)(2) (.(MeOH)(2)). The crystal structures of .(DMF)(2) and .(DMF)(2) exhibit an unsymmetrical central U(2)O(2) core involving bridging alkoxy- and hydroxy-oxygen atoms. The geometry around the uranium center in .(DMF)(2) and .(DMF)(2) is that of a distorted pentagonal bipyramid with the solvent molecule occupying the fifth coordination site. The flexible nature of the ligand backbone is more pronounced in .(DMF)(2) compared to .(DMF)(2), yielding two molecules per unit cell in different conformations. Under similar reaction conditions, using ethylenediamine as a base, the respective Salen-based uranyl compounds, [UO(2)(Salen)(MeOH)] () and [UO(2)(Bu(t)(2)-Salen)(MeOH)] () are obtained due to transamination of the ligand backbone. Complexes .(MeOH)(2) and .(MeOH)(2) when reacted with an excess of ethylenediamine failed to yield the respective Salen-based complexes, and , respectively. The new compounds have been characterized using solution (NMR and UV-Vis) and solid-state (IR, X-ray crystallography) techniques. Hydrolysis of .(MeOH)(2) and .(MeOH)(2) in the pH range 1-14 was studied using UV-Vis spectroscopy and compared with the hydrolysis of and [UO(2)(Salophen)(MeOH)] (). A two-phase extraction study suggests quantitative removal of uranyl ions from the aqueous phase at higher pH conditions.