Synthesis and structural features of Np(VI) and Pu(VI) isophthalates

Resumo

New An(VI) isophthalate complexes [PuO₂(C₈H₄O₄)] (I), Cs₂[(NpO₂)₂(C₈H₄O₄)₃]·4H₂O (II), [H₃O]₂[(NpO₂)₂(C₈H₄O₄)₃]·nH₂O (III), and [H₃O][NpO₂(C₈H₄O₄)(C₈H₅O₄)]·2H₂O (IV) with the An(VI): Lig ratios of 1: 1 (I), 1: 1.5 (II, III), and 1: 2 (IV) were synthesized and studied by single crystal X-ray diffraction. In complex I, the coordination polyhedron of the Pu(1) atom is a pentagonal bipyramid whose equatorial plane is formed by the oxygen atoms of four [C₈H₄O₄]^2– anions. The coordination capacity of the ligand in complex I is maximal among compounds I–IV and equal to 5, with each [C₈H₄O₄]^2– anion binding four PuO₂²⁺ cations into electrically neutral layers. In the structures of II and III, the coordination polyhedra of the Np(1) atoms are hexagonal bipyramids whose equatorial planes are formed by the oxygen atoms of three [C₈H₄O₄]^2– anions. Two crystallographically independent [C₈H₄O₄]^2– anions exhibit the coordination capacity equal to 4, each binding two NpO₂²⁺ cations in the chelate fashion. As a result, doubled anionic layers are formed in the crystals of II and III. Outer-sphere cations influence the packing of doubled layers in the crystals: Complex II crystallizes in the monoclinic system, and complex III, in the orthorhombic system. In the structure of IV, the coordination polyhedron of the Np(1) atom is a hexagonal bipyramid whose equatorial plane is formed by the oxygen atoms of two [C₈H₄O₄]^2– anions and one [C₈H₅O₄]^– anion. The crystallographically independent bridging anion [C₈H₄O₄]^2– exhibits the coordination capacity equal to 4 and binds in the chelate fashion two NpO₂²⁺ cations to form chains, and the independent hydrogen isophthalate anion [C₈H₅O₄]^– binds one neptunyl(VI) cation in the chain in the chelate fashion, exhibiting the coordination capacity equal to 2.