Effects of Large Halides on the Structures of Lanthanide(III) and Plutonium(III) Borates

Reactions of LnBr3 or LnOI with molten boric acid result in formation of Ln­[B5O8(OH)­(H2O)2Br] (Ln = La–Pr), Nd4[B18O25(OH)13Br3], or Ln­[B5O8(OH)­(H2O)2I] (Ln = La–Nd). Reaction of PuOI with molten boric acid yields Pu­[B7O11(OH)­(H2O)2I]. The Ln­(III) and Pu­(III) centers in these compounds are found as nine-coordinate hula-hoop or 10-coordinate capped triangular cupola geometries where there are six approximately coplanar oxygen donors provided by triangular holes in the polyborate sheets. The borate sheets are connected into three-dimensional networks by additional BO3 triangles and/or BO4 tetrahedra that are roughly perpendicular to the layers. The room-temperature absorption spectrum of single crystals of Pu­[B7O11(OH)­(H2O)2I] shows characteristic f–f transitions for Pu­(III) that are essentially indistinguishable from Pu­(III) in other compounds with alternative ligands and different coordination environments.