Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States

摘要

Pentavalent actinyl nitrate complexes An(V)O(2)(NO3)(2)(- )were produced by elimination of two NO2 from An(III)(NO3)(4)(-) for An = Pu, Am, Cm, Bk, and Cf. Density functional theory (B3LYP) and relativistic multireference (CASPT2) calculations confirmed the AnO(2)(NO3)(2)(-) as An(V)O(2)(+) actinyl moieties coordinated by nitrates. Computations of alternative An(III)O(2)(NO3)(2)(-) and An(IV)O(2)(NO3)(2)(-) revealed significantly higher energies. Previous computations for bare AnO(2)(+) indicated AnVO(2)(+) for An = Pu, Am, Cf, and Bk, but (CmO2+)-O-III: electron donation from nitrate ligands has here stabilized the first CmV complex, (CmO2)-O-V(NO3)(2)(-). Structural parameters and bonding analyses indicate increasing An-NO3 bond covalency from Pu to Cf, in accordance with principles for actinide separations. Atomic ionization energies effectively predict relative stabilities of oxidation states; more reliable energies are needed for the actinides.