Complex formation of uranium(VI) with 4-hydrosy-3-methoxybenzoic acid and related compounds

The complex formation of uranium(VI) with 4-hydroxy-3-methoxybenzoic acid as well as with benzoic acid and 3-hydroxybenzoic acid was studied. In aqueous solution weak carboxylic 1:1 complexes, in which the carboxyl group is bidentately coordinated to the metal atom, are formed. The logarithmic stability constants of these complexes regarding the reaction of the uranyl ion with the single charged anion of the respective ligands are 2.78 ± 0.04, and 2.71 ± 0.04 at an ionic strength of 0.1 mol/l (NaClO4) and at 25 °C.
Bis(4-hydroxa-3-methoxybenzoato)dioxouranium(VI) was obtained as a crystalline complex if the concentrations of the starting compounds for the synthesis are increased. The monoclinic compound has a reflections-rich X-ray powder diffraction pattern. The lattice constants are a = 13.662(9) Å, b = 21.293(7) Å, c = 11.213(3) Å, b = 107.49(4)°, and V = 3111(2) Å3.