CROWN COMPOUNDS FOR ANIONS - THE NATURE OF CHEMICAL-BONDS IN THE COMPLEXES OF HALIDE ANIONS WITH CYCLIC TRIMERIC PERFLUORO-O-PHENYLENEMERCURY AND SOME OF ITS ANALOGS

Geometries and electronic structures of the complexes of halide anions with cyclic trimeric o-phenylenemercury, (o-C6H4Hg)(3), perfluoro-o-p henylenemercury, (o-C6F4Hg)(3), vinylenemercury, (C2H2Hg)(3), and perf luorovinylenemercury, (C2F2Hg)(3), Were modelled by the MNDO method. C alculations were performed for [L-X](-) semisandwich complexes, [X-L-X ](2-) bipyramidal complexes, and [L-X-L](-) sandwich complexes (where X = Hal, L is a mercury-containing macrocycle). Based on the results o f calculations, we concluded that it was advantageous to describe the chemical bonding between halide anions and mercury-containing macrocyc les in terms of generalized chemical bonds, which were successfully us ed for x-complexes of transition metals. In the [L-X](-) semisandwich complexes, the halide anion and the metallacycle are involved in the f ormation of three generalized chemical bonds: one headlight-shaped a-b ond and two two-lobe x-bonds. In the [X-L-X](2-) bipyramidal complexes , each halide anion forms three generalized chemical bonds with the ma crocycle. It is possible because the macrocycle L has unoccupied molec ular orbitals suitable for the formation of such bonds; these MOs cons ist mainly of the orbitals of mercury atoms directed toward both the u pper and lower halogen atoms. In the [L-X-L](-) sandwich complexes, th e halide anion cannot be bonded to each ring via three bonds, and, hen ce, an unsymmetrical structure is formed, in which the rings are Locat ed at different distances from the central atom: the [L-X](-) semisand wich complex solvated by macrocycle L.