Metal-assembled cobalt(II) resorc[4]arene-based cage molecules that reversibly capture organic molecules from water and act as NMR shift reagents

The complex Co(4)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. H-1 NMR studies of Co(4)1(2)(8-). guest complexes demonstrate inclusion of nonpolar hydrocarbons, substituted phenyls, alcohols, halogen-containing hydrocarbons, and polar organic molecules. The complex Co(4)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 Co(4)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 Ba-4[Co(4)1(2). C6H5C2H5] shows a disordered guest molecule encapsulated within the cavity of Co(4)1(2)(8-). The cavity dimensions, bond lengths, and bond angles of Ba-4[Co(4)1(2). C6H5C2H5] are very similar to those determined in Ba-4[Co(4)1(2). 6H(2)O].