Guest Exchange in Halogenated Host-Guest Compounds: Structures and Kinetics

The host compounds tetralds(4-bromophenyl) ethylene, H1, and its iodo-analogue (H2) form inclusion compounds with the guests 1,2-dichloroethane (DCE), methyl iodide (MeI), benzene (BEN), and piperidine (PIP). The structures of the host guest compounds have been elucidated and a series of exchange experiments on these compounds were performed by exposing their single crystals to the vapors of different guests. The kinetics of the exchange was monitored by NMR spectroscopy, and the reactions were interrupted and the structures of the inclusion compounds containing both the incoming and outgoing guests were solved. In the case of 1.5H1 center dot DCE exchanged with MeI, the intermediate structure yields a unit cell which has quadrupled in volume and shows both DCE and MeI in distinct, different locations. In the case of BEN being exchanged with PIP, the guests occupy the same site, and the mechanism is one of isomorphous replacement.