Uranyl complexes with the pyridine-2,6-dicarboxylato ligand: new dinuclear species with μ-η 2,η 2-peroxide, μ 2-hydroxide or μ 2-methoxide bridges

Abstract

Pyridine-2,6-dicarboxylic acid (LH 2) reacts with uranyl nitrate in the presence of triethylamine to form either mononuclear or new dinuclear complexes, the latter being different from the species obtained up to now with this ligand under different experimental conditions. In all cases, the uranium atom is bound to the pyridine nitrogen atom and to one oxygen atom from each carboxylate group. Its coordination sphere is completed either by a second ligand L 2−, giving the 1:2 mononuclear complex 1, by a water molecule and a bridging μ-η 2,η 2-peroxide ion in the dinuclear complex 2, by two bridging μ 2-hydroxide ions in 3 and 4 or by two bridging μ 2-methoxide ions in 5. Complex 5 provides the first example of uranyl-bridging by methoxide ions to be crystallographically characterized. Extended hydrogen bonded networks involving the carboxylate groups, the bridging species and the counter-ions and solvent molecules are formed in all cases, resulting in chain, ribbon or sheet assemblages.