Structure of the {U(13)} polyoxo cluster U(13)O(8)Cl( x )(MeO)(38–x ) (x = 2.3, MeO = methoxide)

The structure of a new type of polyoxo cluster complex that contains thirteen uranium atoms, {U(13)}, is reported. The complex crystallized from methanol containing tetra­valent uranium (U(IV)) with a basic organic ligand, and was characterized as di­chloridoocta­cosa-μ(2)-methano­lato-octa­kis­(methano­lato)octa-μ(4)-oxido-trideca­uranium, [U(13)(CH(3)O)(35.7)Cl(2.3)O(8)] or [U(13)(μ(4)-O(oxo))(8)Cl( x )(MeO)(38–x )] (x = 2.3, MeO = methoxide) (I), by single-crystal X-ray diffraction. The characterized {U(13)} polyoxo cluster complex (I) possesses a single cubic uranium polyhedron at the centre of the cluster core. To the best of our knowledge, this is the very first example of a polyoxo actinide complex that bears a single cubic polyhedron in its structure. The cubic polyhedron in I is well comparable in shape with those in bulk UO(2). The U—O bonds in the cubic polyhedron of I are, however, significantly shorter than those not only in bulk UO(2) but also in another analogue in the {U(38)} cluster. This shortening of U—O bonds, together with BVS calculations and the overall negative charge (2−) of I, suggests that the central uranium atom in I, which forms the single cubic coordination polyhedron, is presumably oxidized to the penta­valent state (U(V)) from the original tetra­valent state (U(IV)). Complex I is, hence, the first example of a polyoxo cluster possessing a single cubic coordination polyhedron of U(V).