Synthesis and structure of dimeric complexes of U(VI) and Np(VI) with isophthalic acid anions, {AnO2[C6H4(COO)(COOH)]2(H2O)}2

Two previously unknown isophthalate complexes [AnO2(C8H5O4)2(H2O)]2 [An(VI) = U, Np] were synthesized, and their structure was studied by single crystal X-ray diffraction. The compounds are isostructural. Their structural unit is a centrosymmetrical dimeric complex. The coordination surrounding of the An(VI) atoms in the structure is formed by the O atoms of three acidic anions [C8H5O4]- and of water molecules; the coordination polyhedra are pentagonal bipyramids with the oxygen atoms of the AnO2 groups in the apical positions. One of the two independent [C8H5O4]- anions is bidentate chelating, and the other is bidentate bridging. The different functions of the anions influence the bond lengths in the coordination polyhedra of the An(VI) atoms. The 3D network of hydrogen bonds additionally stabilizes the crystal structure, and the hydrogen bonding influences the geometric and conformational characteristics of the dimers. © 2015 Pleiades Publishing, Inc.