Could uranium(XII)hexoxide, UO6 (Oh) exist?

The formally dodecavalent, octahedral U(XII)O(6) is found to be a local energy minimum at Several theoretical levels, including quasirelativistic single-reference (HF, B3LYP, MP2 and CCSD(T)) and multireference CI approaches. The fully relativistic, single-configuration Dirac-Fock (DF) approach gives similar U-O bond lengths but has one imaginary frequency. In this hypothetical compound the largest formal oxidation state of uranium would be increased from +VI to +XII. (C) 2000 Elsevier Science B.V.