From monomers to polymers: steric and supramolecular effects on dimensionality of coordination architectures of heteroleptic mercury(ii) halogenide–tetradentate Schiff base complexes

Abstract

In this study, neutral mercury(II) complexes of the composition [Hg(L1)(μ-Cl)₂Hg₃Cl₆]_n (1), [Hg(L1)(μ-Br)₂HgBr₂] (2), [Hg(L3)Br₂] (2a), [Hg(L1)I₂] (3), [Hg(L2)Cl₂]·CH₃OH (4) and [Hg(L2)(μ-Br)HgBr₃]₂ (5) (L1 = benzilbis((pyridin-2-yl)methylidenehydrazone); L2 = benzilbis((acetylpyridin-2-yl)methylidenehydrazone)) are described. Single-crystal X-ray crystallography showed that the molecular complexes can aggregate into larger entities depending upon the anion coordinated to the metal centre. Iodide gives discrete monomeric complexes, bromide generates a 1D coordination polymer formed through Hg–Br–Hg bridges and chloride gives rise to an inorganic–organic hybrid material. The significant differences in the reaction conditions indicate that the anions exert a substantial influence on the formation of the compounds – smaller anions show a larger potential for bridging metal ions and forming coordination polymers. A minute increase in the bulkiness of the ligand (two extra methyl substituents in L2) dramatically changes the coordination architectures, and leads to the formation of monomeric (chloride and iodide) and oligomeric (bromide) structures, rather than polymeric structures. The noncovalent C–H/π and π-hole interactions observed in the solid state architecture of some complexes have been rationalized by means of theoretical DFT calculations.