The influence of counter ion and ligandmethyl substitution on the solid-state structures and photophysical properties of mercury(ii) complexes with (E)-N-(pyridin-2-ylmethylidene)arylamines

Abstract

Ten neutral monomeric, dimeric and polymeric mercury(II) complexes of compositions HgX₂L (3, 8), [HgX₂L]₂ (1, 2, 4–6 and 7), [Hg(NO₃)₂L]_n (9) and {[Hg(N₃)₂L]₂}_n (10) where X = chloride, bromide, iodide, nitrate and azide, and L = (E)-N-(pyridin-2-ylmethylidene)arylamine, are described. Compounds 1–10 were characterized by elemental analyses, and IR and ¹H NMR spectroscopic studies. The solution-state photophysical properties of the complexes are highly dependent on the anions as seen in the fluorescence emission features. 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, chloride and bromide generate binuclear complexes formed through Hg–X–Hg bridges, while nitrate and azide lead to 1D coordination polymers. The significant differences in the observed aggregation patterns of the compounds indicate that the anions exert a substantial influence on the formation of the compounds. A further influence upon supramolecular aggregation is the presence of methyl substituents in L³ and L⁴, which generally enhances the probability of forming supramolecular π⋯π interactions involving the five-membered C₂N₂Hg chelate rings in their crystal structures.