| Abstract
| - The complex Co4128- is a tetranuclear cobalt(II) cage compound that assembles in aqueous solutions above pH4 and is capable of encapsulating a variety of organic guest molecules, for example, benzene, hexane, chlorobutane,butanol, and ethyl acetate. Ligand 1 is a resorc[4]arene-based molecule with iminodiacetate moieties appended toits upper rim. 1H NMR studies of Co4128-·guest complexes demonstrate inclusion of nonpolar hydrocarbons,substituted phenyls, alcohols, halogen-containing hydrocarbons, and polar organic molecules. The complex Co4128-acts as an NMR shift reagent and causes substantial upfield isotropic hydrogen shifts (−30 to −40 ppm) in theguest molecule and separation of the guest hydrogen chemical shifts by typically 12 ppm. The complex Co4128-will encapsulate molecules with fewer than eight atoms in a linear chain, mono- and disubstituted benzenes, andpolar molecules with greater than two carbon atoms. The solid-state structure of Ba4[Co412·C6H5C2H5] shows adisordered guest molecule encapsulated within the cavity of Co4128-. The cavity dimensions, bond lengths, andbond angles of Ba4[Co412·C6H5C2H5] are very similar to those determined in Ba4[Co412·6H2O].
- Cobalt(II) ions assemble two resorcinarenes into a cage molecule. When the water-soluble cages are formed in the presence of organic molecules, such as aromatics, alkanes, haloalkanes, and oxygen-containing alkanes, the organic molecules are trapped within the cavity of the cage. Because of the paramagnetic nature of the cage, the 1H NMR signals of the guest are shifted and separated. The guests can be released by lowering the pH to below 4.
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