Synthesis and crystal structure of An(VI) complexes with cyclobutanecarboxylic acid anions, [AnO2(C4H7COO)2(H2O)2] (An = U, Np) and [AnO2(C4H7COO)2(H2O)] (An = Np, Pu)

Abstract

New complexes of hexavalent actinides with cyclobutanecarboxylic acid (Hcbc) anions, dihydrates [AnO₂(cbc)₂(H₂O)2] [An = U (I) or Np (II)] and monohydrates [AnO₂(cbc)₂(H₂O)] [An = Np (III) or Pu (IV)], were synthesized and studied by single crystal X-ray diffraction. The crystal structure of dihydrates I and II consists of discrete complexes. The coordination polyhedron (CP) of An(VI) in the dihydrates is a distorted hexagonal bipyramid with oxygen atoms of two C₄H₇COO^– anions coordinated in the bidentate chelate fashion and two water molecules in the equatorial plane and two oxygen atoms of AnO₂²⁺ cations in the apical positions. The geometry of the An(VI) CP is influenced by O_w–H···O_cbc hydrogen bonding. Monohydrates III and IV have a chain structure. The CP of An(VI) is a pentagonal bipyramid with oxygen atoms of three C₄H₇COO^– anions and one water molecule in the equatorial plane. Two crystallographically independent C4H7COO–anions are coordinated in different fashions: one in the bidentate chelate fashion and the other, in the bidentate bridging fashion, linking the AnO₂²⁺ cations into electrically neutral chains oriented along the [010] direction in the crystal. The structure of the chain is strongly influenced by hydrogen bonding.