Formation of Dinuclear, Macrocyclic, and Chain Structures from HgI₂ and a Semirigid Benzimidazole-Based Bridging Ligand:  An Example of Ring-Opening Supramolecular Isomerism

The reactions of HgI₂ with the semirigid ditopic ligand 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene (bbimms) afforded three new complexes, [Hg₂(μ-I)₂I₂(bbimms)] (1), [Hg₂I₄(bbimms)₂] (2), and catena-poly[HgI₂(bbimms)] (3). The ligand and all complexes have been structurally characterized by single-crystal X-ray diffraction. 1 is a triply bridged dinuclear complex comprised of two Hg(II) ions, one bridging ligand, two bridging I^- anions, and two terminal I^- anions. 2 is a dinuclear metallamacrocycle comprised of two Hg(II) ions, two bridging ligands, and four terminal I^- anions, while 3 is a helical chain with the repeating unit of HgI₂(bbimms). 2 and 3 can be classified as supramolecular isomers, and both are related to the triply bridged precursor 1 via the addition of one more ligand in a ring-opening process.