Metal-Assembled Cobalt(II) Resorc[4]arene-Based Cage Molecules That Reversibly Capture Organic Molecules from Water and Act as NMR Shift Reagents

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Abstract

The complex Co4 1(2)8- is a tetranuclear cobalt(II) cage compound that assembles in aqueous solutions above pH 4 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 to its upper rim. 1H NMR studies of Co4 1(2)8-.guest complexes demonstrate inclusion of nonpolar hydrocarbons, substituted phenyls, alcohols, halogen-containing hydrocarbons, and polar organic molecules. The complex Co4 1(2)8- acts as an NMR shift reagent and causes substantial upfield isotropic hydrogen shifts (-30 to -40 ppm) in the guest molecule and separation of the guest hydrogen chemical shifts by typically 12 ppm. The complex Co4 1(2)8- will encapsulate molecules with fewer than eight atoms in a linear chain, mono- and disubstituted benzenes, and polar molecules with greater than two carbon atoms. The solid-state structure of Ba4[Co4 1(2).C6H5C2H5] shows a disordered guest molecule encapsulated within the cavity of Co4 1(2)8-. The cavity dimensions, bond lengths, and bond angles of Ba4[Co4 1(2).C6H5C2H5] are very similar to those determined in Ba4[Co4 1(2).6H2O].

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