Mercury(II) halide adducts of a dicarboxylate-like ligand: Crystal structures of polymeric mercury(II) complexes with 1,4-diazoniobicyclo[2.2.2]octane-1,4-diacetate

Three mercury(II) complexes containing double-betaine and halide ligands, (HgCl₂)₂(L¹)] _n (1), (HgBr₂)₂(L¹)(H₂O)₂] _n (2), and 2HgCl₂(HL¹)·Hg₂Cl₆] _n (3) L¹=^–O₂CCH₂N⁺(CH₂CH₂)₃-N⁺H₂CO₂ ^–], have been prepared and shown to have polymeric structures by single-crystal X-ray analysis. Complex (1) exhibits an infinite zigzag chain in which each mercury(II) atom is coordinated by pairs of carboxylate oxygen atoms and chloride ligands in a distorted tetrahedral geometry. In complex (2), the mercury(II) atom is in an unusual square-planar coordination geometry, and weak mercury-ligand and hydrogen bonding extend the structural skeletons into a three-dimensional network. Complex (3) consists primarily of an assembly of HgCl₂(HL¹) moieties and Hg₂Cl₆]^– anions, and the mercury(II) atoms are in planar T-shaped and distorted tetrahedral coordination environments, respectively. The resulting three-dimensional network is based on the cross-linkage of nearly planar, wide ribbons running in thea direction.