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Manipulation of Discrete Nanostructures by Selective Modulation of Noncovalent Forces

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Science  02 May 2014:
Vol. 344, Issue 6183, pp. 499-504
DOI: 10.1126/science.1252120

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Nanotube Engineering

In general, the reversible self-assembly of nanotubes through noncovalent bonding either gives fully assembled or fully disassembled products. Fukino et al. (p. 499, published online 10 April; see the Perspective by Hudson and Manners) developed a system with an intermediate possibility. Hollow nanotube structures were assembled from ferrocene-based tetratopic pyridyl ligands mixed with AgBF4. Through oxidation of the ferrocene groups, the tubes could be cut into stable, large rings and then reversibly reassembled into nanotubes by reduction of the ferrocene groups.

Abstract

Covalent organic synthesis commonly uses the strategy of selective bond cleavage and formation. If a similar approach can be applied stepwisely to noncovalent synthesis, more exotic or challenging nanostructures might become achievable. Here, we report that ferrocene-based tetratopic pyridyl ligands, which can dynamically change their geometry by means of thermal rotation of their cyclopentadienyl rings in solution, assemble with AgBF4 into discrete metal-organic nanotubes with large and uniform diameters. The nanotubes can be cut into metal-organic nanorings through selective attenuation of the inter-nanoring interaction via ferrocene oxidation. The resultant nanorings can be transferred onto inorganic substrates electrostatically or allowed to reassemble to form the original nanotube by the reductive neutralization of their oxidized ferrocene units.

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