Mercury(II) chloride adducts of flexible double betaines: influence of different polymethylene bridges between the quaternary nitrogen atoms

Abstract

Three mercury(II) complexes containing flexible double betaines and chloride ligands, [{Hg₂(L¹)Cl₄}_n]1, [{Hg₄(L²)Cl₈}_n]2 and [{Hg₄(L³)Cl₈}_n]3[^–O₂CCH₂N⁺Me₂(CH₂)_nN⁺Me₂CH₂CO₂^–; n= 2 L¹, 3 L² or 4 L³], have been prepared and shown to have similar polymeric structures by single-crystal X-ray structure analysis. In each complex the mercury atom is co-ordinated by two chloride atoms and a carboxylate oxygen atom in a distorted T-shaped fashion, and additional weak Hg ⋯ O or Hg ⋯ Cl bonds lead to six- or five-co-ordination about mercury and a two-dimensional polymeric structure. Due to the different number of methylene units between the two positively-charged quaternary nitrogen atoms in each flexible double betaine, the complexes exhibit differences in their metal–betaine molar ratios, crystal symmetries and modes of ligation of the carboxylate groups. Complexes 1 and 3 crystallize in the same monoclinic space group p2₁/n with Z= 2, while 2 is monoclinic, space group C2 with Z= 2. With maximum separation of the two carboxymethyl groups, the flexible double betaines in 1 and 3 are each located at an inversion centre, while that in 2 lies on a C₂ axis. The carboxylate groups co-ordinate to the metal atoms in the unidentate mode in 1, and O-bridging mode in 2 and 3.