Selective Metallic Tube Reactivity in the Solution-Phase Osmylation of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes have been reacted with osmium tetroxide (OsO₄) in solution in the presence of O₂ and UV irradiation at 254 nm. We observe one main structural motif, namely thickly coated nanotube structures, densely covered with OsO₂, consisting of multiple bundles of derivatized tubes. In a few instances, bridging uncoated tubes, connecting these thickly coated structures, incorporate a number of smaller nanotube bundles, projecting out from the larger functionalized aggregates of tubes. 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. Extensive characterization of these osmylated adducts has been performed using a variety of electron microscopy and optical spectroscopy techniques.