Nanoscale Tubules in Uranyl Selenates

摘要

Since the discovery of carbon nanotubes in 1991,[1] a great deal of attention has been devoted to the synthesis and characterization of inorganic nanotubes.[2] In particular, oxidic nanotubes exhibit interesting properties and hold promise for potential applications. Such nanotubes have been prepared for a variety of chemical systems, including vanadium oxides,[3] titania,[4] niobium oxides,[5] and rare-earth oxides.[6] One of the most accepted models of formation of nanotubes is the rolling and folding-up of single-layer sheets of the corresponding prototype lamellar materials.[2c], [7] Thus, it is generally possible to prepare nanotubes and nanoscrolls from any lamellar material that can be exfoliated into separate nanosheets.[7] Among inorganic materials, layered structures are especially prevalent for hexavalent uranium oxo compounds[8] owing to the strong tendency of the U6+ ion to form linear uranyl ions, UO22+. This tendency leads to a highly anisotropic distribution of chemical bonds within {UVIOn} coordination polyhedra,[9] and, in particular, favors their condensation through longer UO bonds lying in the equatorial plane relative to the uranyl ions. Despite the abundance of layered structures for UVI oxo compounds, there are no reports of their ability to form tubular objects. Here, we report the synthesis and structure of K5[(UO2)3(SeO4)5](NO3)(H2O)3.5 (1), which is a new compound based upon nanoscale uranyl selenate tubules.