VOLUME 5, NUMBER 10, OCTOBER 2005 © Copyright 2005 by the American Chemical Society
Carbon Nanotube Inner Phase Chemistry: The Cl- Exchange SN2 Reaction Mathew D. Halls and Krishnan Raghavachari* Department of Chemistry, Indiana UniVersity, Bloomington, Indiana 47405-7102 Received April 19, 2005; Revised Manuscript Received May 26, 2005
ABSTRACT Density functional calculations have been carried out to investigate the nature of the inner phase of a (6,6) carbon nanotube, using the Clexchange SN2 reaction as an indicator. Inside the carbon nanotube the classical barrier height increases by 6.6 kcal/mol due to the nanotube polarizability. This suggests that the inner phase environment can be considered a form of solid solvation, offering the possibility of obtaining altered guest properties and reactivity through dielectric stabilization.
Molecular1 and extended systems with internal voids, capable of accommodating atomic and molecular guests, have received widespread attention because of their potential use in catalytic, storage, sensing, and separation applications. Discrete supramolecular host systems have been shown to perform catalysis and other functions such as stabilizing reactive species through encapsulation.2-6 The success of inorganic zeolites,7-10 has spurred efforts directed toward the design of periodic nanoporous organic hosts.11-13 Following the report by Iijima in 1991,14 carbon nanotubes have been shown to possess remarkable mechanical15-18 and electronic properties.19-22 Carbon nanotubes are graphene cylinders with enormous aspect ratios and are well-defined in terms of chirality and tube diameter. Structurally, their characteristics may be considered as being intermediate to the molecular and extended solid regimes. Ebbesen and coworkers23 studied the filling of carbon nanotubes with various materials and determined that materials with low surface * Corresponding author. E-mail:
[email protected]. 10.1021/nl050722u CCC: $30.25 Published on Web 09/20/2005
© 2005 American Chemical Society
tension, such as water and organics, would be easily drawn into the inner phase of a carbon nanotube. Carbon nanotubes have been filled with a variety of materials,24-27 ranging from ionic species such as KI,28 to a wide selection of organics,29 such as o-carborane,30 C60 and higher fullerenes,31-33 and even endohedral species.34 To-date, the main objective for introducing guest species into the inner phase of carbon nanotubes has been to modulate the native electronic structure of the nanotube; however, reports of inner phase molecule reactions are beginning to appear in the literature. In one of the earliest reports of nanotube inner phase chemistry, Ugarte et al.35 filled carbon nanotubes with AgNO3 and then created Ag nanoparticles in the inner phase by electron-beam mediated reduction. Carbon nanotube encapsulated CoFe2O4 nanowires have been synthesized using the confinement effect of the carbon nanotube inner phase.36 Most recently, Britz, Khlobystov and co-workers37 polymerized C60O inside carbon nanotubes yielding a peapod polymer that differed topologically from the bulk polymer.
Table 1. Gas Phase and (6,6) Carbon Nanotube Inner Phase Critical Point Geometric Parameters and Energies for the Cl- Exchange SN2 Reaction Computed Using the B3-LYP/(6-31+G*:3-21G) Level of Theory
separated Cl- and H3CCl Cla-...H3CClb [Cla...H3C...Clb]q separated Cl- and H3CCl Cla-...H3CClb [Cla...H3C...Clb]q a
RC-H (Å)
