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 Co4128- 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 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 the
guest 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, and
polar molecules with greater than two carbon atoms. The solid-state structure of Ba4[Co412·C6H5C2H5] shows a
disordered guest molecule encapsulated within the cavity of Co4128-. The cavity dimensions, bond lengths, and
bond angles of Ba4[Co412·C6H5C2H5] are very similar to those determined in Ba4[Co412·6H2O].