Interaction of metal ions with humic-like models. Part 6. Molecular structure, spectral and thermal properties of diaquabis(2,6-dimethoxybenzoato)dioxouranium(VI) monohydrate

Abstract The crystal and molecular structure of [UO 2 (DMB) 2 (H 2 O) 2 ]·H 2 O (DMB = 2,6-dimethoxybenzoate), complex I , has been detcrmined by X-ray diffraction and refined to a final R value of 0.0411. The compound belongs to the space group P 2 1 / a with cell constants a = 12.649(4), b = 14.418(5), c = 13.460(4) A and Z = 4. As in the analogous complex [UO 2 (DHB) 2 (H 2 O) 2 ]·8H 2 O (DHB = 2,6- dihydroxybenzoate), compound II , the uranyl ion is bound to two bidentate carboxylate groups and two water molecules, but the point-symmetry is lower because the carboxylates, and the water molecules, are in vicinal positions. The lack of hydrogen- bonds between carboxylate groups and ortho -methoxy substituents and, possibly, steric factors account for the rotation of the phenyl rings with respect to the equatorial plane of the metal, the dihedral angle between the ‘best planes’ being about 77°. Detectable changes in the bond distances and angles within the carboxylate groups are produced by the non-planarity of the ligand. Spectroscopic and thermal properties of complexes I and II are also compared.