Crown compounds for anions:: Sandwich and half-sandwich complexes of cyclic trimeric perfluoro-o-phenylenemercury with polyhedral closo[B10H10]2- and closo-[B12H12]2- anions

It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4- Hg)(3) (1) is capable of binding closo-[B10H10](2-) and closo-[B12H12](2-) anions to form complexes [{(o-C6F4Hg)(3)}(B10H10)](2-) (2), [{(o-C6F4Hg)(3)}(2)(B10H10)](2-)(3), [{(o-C6F4Hg)(3)}(B12H12)](2-) (4), and [{(o-C6F4Hg)(3)}(2)(B12H12)](2-) (5). According to IR data, the bonding of the [B10H10](2-) and [B12H12](2-) ions to the macrocycle in these complexes is accomplished through the formation of B-H-Hg bridges. Complexes 2, 3, and 5 have been isolated in analytically pure form and have been characterized by spectroscopic means. X-ray diffraction studies of 3 and 5 have revealed that these compounds have unusual sandwich structures, in which the polyhedral dianion is located between the planes of two molecules of 1 and is bonded to each of them through two types of B-H-Hg bridges. One type is the simultaneous coordination of a B-H group to all three Ha atoms of the macrocycle. The other type is the coordination of a B-H group to a single Hg atom of the cycle. According to X-ray diffraction data, complex 2 has an analogous but half-sandwich structure. The obtained complexes 2-5 are quite stable; their stability constants in THF/acetone (1:1) at 20 degreesC have been determined as 1.0 x 10(2) L mol(-1), 2.6 x 10(3) L-2 mol(-2), 0.7 x 10(2)Lmol(-1), and 0.98 x 10(3) L-2 mol(-2), respectively.