Organomercury macrocyclic receptors

One of the earliest known organomercury macrocycles was the trimer of oriho-phenylene mercury, (o-C6H4Hg)3, known from X-ray diffraction studies to have a planar cyclic structure, 1 [1, 2]. It has recently been found, with the aid of Hg NMR spectroscopy, that this compound forms complexes with hahde anions (Cl, Br and I ) in dichloromethane solution, but the complexes could not be isolated in solid state [3]. The fluorinated analog (o-C6F4Hg)3, 2, is a much better electron acceptor and forms stable complexes with the same halide anions these could be 

The same fluorinated mercuracycle links thiocyanate anions (in acetone solution) and the tetra-n-butylammonium salt of [(n-C6F4Hg)3SCN] has been isolated and structurally characterized [6]. The crystal structure contains a helical chain of alternating (o-C6F4FIg)3 molecules and SCN ions. The stacks are held by sulfur atoms at Hg- -S distances in the range 3.06-3.36 A, with one longer at 3.87 A. Thus, both host-guest complexation and supramolecular self-assembly if observed with these compounds. 

Another macrocyclic organomercury receptor for halide anions is the pen tamer [HgC(CF3)2]s, 3, which contains a nearly planar HgsCs ring [7]. It reacts with tetraphenylphosphonium chloride to form a 1 2 complex, [HgC(CF3)3]5CF -, with each chlorine coordinated to all five mercury atoms (ave Hg- - Cl 3.284 A above and 3.221 A below the ring), the macrocycle being stacked between the two halide anions [8]. 

The nature of chemical bonds between the ring metal atoms and the incorporated anions has been analyzed theoretically by the MNDO method [9]. 

Tri- and tetranuclear mercuracarbaboranes were recently prepared and were found to bind halide and other anions by forming host-guest complexes such as 4 and 5 [10-19]. The subject has recently been covered by an excellent review [20]. 

---