Carboracycles were originally prepared for use as precursors to cyclic metallacarboranes and in molecular recognition studies involving localized hydrophobic bonding. A novel application under investigation is the interaction of water-soluble carboracycles with hydrophobic organic guests in aqueous media. Thus water-soluble carboracycles with hydrophobic cavities may support the solubilization of hydrophobic carborods (rotaxane formation), fullerenes, hydrocarbons, and other species through localized hydrophobic bonding (see Figure 2).

In addition, carboracycles may be used as molecular scaffolding for the support of functional groups (i.e., hydroxyl, carboxyl, phosphonium or ammonium) which may demonstrate novel association phenomena in solution through both covalent (metal complexation) and coulombic means. Hydrogen-bonding or coulombic interactions between cycles could also be manifested in the solid sate as either edge-pairing or ring-stacking (see Figure 3).

          The size and geometry of the cycles, the identity of the carborane fragments, and the nature of the linking groups can all be varied in a controlled fashion to give a variety of novel structures. It is possible to introduce reactive centers into the cycles, either as linker-group modifiers or by functionalization of the carborane icosahedra, thus opening the way to large multivalent species capable of interaction with either transition metal centers or other electrophilic guests. For example, the linker alpha,alpha'-2,6-lutidylene-bridged meta-carborane cyclic dimer was prepared. Subsequent oxidation of the lutidylene produced the bis(N-oxide) carboracycle derivative. Further reactions of this sort are currently under investigation.

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