Abstract
U(VI), Np(VI), and Pu(VI) borates with the formula AnO2[B 8O11(OH)4] (An = U, Np, Pu) have been prepared via the reactions of U(VI) nitrate, Np(VI) perchlorate, or Pu(IV) or Pu(VI) nitrate with molten boric acid. These compounds are all isotypic and consist of a linear actinyl(VI) cation, AnO22+, surrounded by BO 3 triangles and BO4 tetrahedra to create an AnO 8 hexagonal bipyramidal environment. The actinyl bond lengths are consistent with actinide contraction across this series. The borate anions bridge between actinyl units to create sheets. Additional BO3 triangles and BO4 tetrahedra extend from the polyborate layers and connect these sheets together toform a three-dimensional chiral framework structure. UV-vis-NIR absorption and fluorescence spectroscopy confirms the hexavalent oxidation state in all three compounds. Bond-valence parameters are developed for Np(VI).