Deviation Between the Chemistry of Ce(IV) and Pu(IV) and Routes to Ordered and Disordered Heterobimetallic 4f/5f and 5f/5f Phosphonates

The heterobimetallic actinide compound UO2Ce(H2O)[C6H4(PO3H)2]2·H2O was prepared via the hydrothermal reaction of U(VI) and Ce(IV) in the presence of 1,2-phenylenediphosphonic acid. We demonstrate that this is a kinetic product that is not stable with respect to decomposition to the monometallic compounds. Similar reactions have been explored with U(VI) and Ce(III), resulting in the oxidation of Ce(III) to Ce(IV) and the formation of the Ce(IV) phosphonate, Ce[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O, UO2Ce(H2O)[C6H4(PO3H)2]2·H2O, and UO2[C6H4(PO3H)2](H2O)·H2O. In comparison, the reaction of U(VI) with Np(VI) only yields Np[C6H4(PO3H)2]2·2H2O and aqueous U(VI), whereas the reaction of U(VI) with Pu(VI) yields the disordered U(VI)/Pu(VI) compound, (U0.9Pu0.1)O2[C6H4(PO3H)2](H2O)·H2O, and the Pu(IV) phosphonate, Pu[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O. The reactions of Ce(IV) with Np(VI) yield disordered heterobimetallic phosphonates with both M[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O (M = Ce, Np) and M[C6H4(PO3H)2]2·2H2O (M = Ce, Np) structures, as well as the Ce(IV) phosphonate Ce[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O. Ce(IV) reacts with Pu(IV) to yield the Pu(VI) compound, PuO2[C6H4(PO3H)2](H2O)·3H2O, and a disordered heterobimetallic Pu(IV)/Ce(IV) compound with the M[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O (M = Ce, Pu) structure. Mixtures of Np(VI) and Pu(VI) yield disordered heterobimetallic Np(IV)/Pu(IV) phosphonates with both the An[C6H4(PO3H)(PO3H2)][C6H4(PO3H)(PO3)]·2H2O (M = Np, Pu) and An[C6H4(PO3H)2]2·2H2O (M = Np, Pu) formulas.