THE ROLES OF N-COORDINATION AND O-COORDINATION IN THE CRYSTAL AND MOLECULAR-STRUCTURES OF URANYL COMPLEXES WITH ANTHRANILIC AND PYRAZINIC ACIDS

Oxonium tris(2-aminobenzenecarboxylato) dioxouranium(VI) monohydrate c rystals contain monomeric molecules composed of a UO2 group (U-O 1.755 Angstrom mean; 178.3 degrees) and six oxygen atoms in the equatorial plane (U-O mean 2.456 Angstrom) donated by three bidentate carboxylic groups of anthranilic acid molecules. The coordination polyhedron is t hus a hexagonal bipyramid involving solely O-coordination. Monoaquobis (2-pyrazinecarboxylato) dioxouranium(VI) dihydrate complex molecules a re monomeric. The UO2 group (U-O mean 1.770 Angstrom, 179.1 degrees) i s surrounded in the equatorial plane by two oxygen atoms (U-O mean 2.3 18 Angstrom), two nitrogen atoms (U-N mean 2.583 Angstrom) donated by pyrazinic acid molecules, and one oxygen atom from a water molecule (U -O 2.405 Angstrom). The coordination polyhedron around the U atom is t hus a pentagonal bipyramid and reflects the propensity for ring N atom s to coordinate with uranyl ions. In the crystal, molecules of both ti tle compounds are held together by systems of hydrogen bonds.