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

Pentavalent actinyl nitrate complexes AnO(NO) were produced by elimination of two NO from An(NO) for An = Pu, Am, Cm, Bk, and Cf. Density functional theory (B3LYP) and relativistic multireference (CASPT2) calculations confirmed the AnO(NO) as AnO actinyl moieties coordinated by nitrates. Computations of alternative AnO(NO) and AnO(NO) revealed significantly higher energies. Previous computations for bare AnO indicated AnO for An = Pu, Am, Cf, and Bk, but CmO: electron donation from nitrate ligands has here stabilized the first Cm complex, CmO(NO). Structural parameters and bonding analyses indicate increasing An-NO 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.