Remarkably High Stability of Late Actinide Dioxide Cations: Extending Chemistry to Pentavalent Berkelium and Californium.

Actinyl chemistry is extended beyond Cm to BkO and CfO through transfer of an O atom from NO to BkO or CfO , establishing a surprisingly high lower limit of 73 kcal mol for the dissociation energies, D[O-(BkO )] and D[O-(CfO )]. CCSD(T) computations are in accord with the observed reactions, and characterize the newly observed dioxide ions as linear pentavalent actinyls; these being the first Bk and Cf species with oxidation states above IV. Computations of actinide dioxide cations AnO for An=Pa to Lr reveal an unexpected minimum for D[O-(CmO )]. For CmO , and AnO beyond EsO , the most stable structure has side-on bonded η -(O ), as An peroxides for An=Cm and Lr, and as An superoxides for An=Fm, Md, and No. It is predicted that the most stable structure of EsO is linear [O=Es =O] , einsteinyl, and that FmO and MdO , like CmO , also have actinyl(V) structures as local energy minima. The results expand actinide oxidation state chemistry, the realm of the distinctive actinyl moiety, and the non-periodic character towards the end of the periodic table.