The focus of our group is generating rational chemical functionalization strategies of carbon nanotubes. In particular, complexation with metal-containing molecular complexes (such as Wilkinson's complex) (a) and solution-phase osmylation (in the presence of O2 and UV irradiation at 254 nm) (b) have been found to be especially sensitive to and selective for nanotube size and for separation of semiconducting vs. metallic tubes, albeit through very different reaction mechanisms. In the first experiment, oxidized carbon nanotubes have been reacted with Wilkinson's complex. It has been found that the Rh metal coordinates to these nanotubes through the increased number of oxygen atoms, forming a hexacoordinate structure around the Rh atom and that this reaction is specific for smaller diameter tubes. In the second experiment, it is believed that OsO2 (a) initially forms on the nanotubes by the preferential covalent sidewall functionalization of metallic nanotubes and (b) subsequently self-aggregates. The formation of an intermediate charge transfer complex is likely the basis for the observed selectivity and reactivity of metallic tubes.
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