Molecular Recognition and Host–Guest Interactions

Abstract

Macrocyclic organomercury compounds have been known for some time, but their ability to bind anionic guests in their cavity was demonstrated relatively recently. This molecular recognition process is somewhat similar to the formation of the crown ether complexes, except that the binding sites of the macrocycle are occupied by metal atoms, able to function as Lewis acids, and therefore to bind halogen and other Lewis base anions. This approach is only in its beginnings and the recent discovery of mercuracarbaboranes as anion binding cyclic receptors gave a new impetus to research in the field.One of the earliest known organomercury macrocycles was the trimer of ovthophenylene mercury, (o-CgH4Hg)3, known from X-ray diffraction studies to have a planar cyclic structure, 1 [I, 21. It has recently been found, with the aid of 199Hg NMR spectroscopy, that this compound forms complexes with halide anions (Cl-, Br-and I-) in dichloromethane solution, but the complexes could not be isolated in solid state [3]. The fluorinated analog (o-CgF4Hg)3, 2, is a much better electron acceptor and forms stable complexes with the same halide anions; these could be 1 2 2.