Incorporation of Mn(II) and Fe(II) into Uranyl Carboxyphosphonates

Abstract

Five heterobimetallic U(VI)/M(II) (M = Mn, Fe) carboxyphosphonates have been synthesized under mild hydrothermal conditions by reacting UO3, triethyl phosphonoacetate, with either Mn(II) or Fe(II) acetate. The manganese reactions yield Mn2[(UO2)6(PO3CH2CO2)3O3(OH)(H2O)2]·16H2O (MnUPAA-1) and [Mn(H2O)6][Mn(H2O)5Mn2(UO2)5(PO3CH2CO2)6(H2O)]·5.75H2O (MnUPAA-2). The addition of boric acid, which lowers the crystallization temperature, allows for the production of a third product, [Mn(H2O)4]2(UO2)3(PO3CH2CO2)2O2 (MnUPAA-3). The iron-containing reactions yield [Fe(H2O)6][UO2(PO3CH2CO2)]2·8H2O (FeUPAA-1) and [Fe(H2O)6][UO2(PO3CH2CO2)H2O]2·4H2O (FeUPAA-2). Four of these five compounds crystallize in low-symmetry space groups; whereas MnUPAA-1 crystallizes in the cubic space group Im3̅ and possesses a remarkably complex open-framework structure containing both UO7 pentagonal bipyramids and UO8 hexagonal bipyramids. MnUPAA-3 adopts a one-dimensional uranium oxide topology that contains both UO6 tetragonal bipyramids and UO7 pentagonal bipyramids. The remaining three compounds solely contain UO7 pentagonal bipyramids.