Synthesis, crystal structures and optical properties of mercury(II) halide compounds with (E)-N-(pyridin-2-ylmethylidene)arylamines: Effect of ligand R-group upon structure

A systematic series of seven mercury compounds of (E)-N-(pyridin-2-ylmethylidene)arylamine (L), where L is a variously R substituted ligand, with the formulations [HgX2L]2: X = Cl; R = 4-CH2CH3 (4), 4-OCH2CH3 (5), 4-Cl (6), 2-CO2CH3 (7), or 4-CO2CH3 (8); X = Br; R = 4-CO2CH3 (9a) and [HgX2L]: X = Br; R = 4-CO2CH3 (9b) and X = I; R = 4-CO2CH3 (10), were synthesized. All compounds have been structurally characterized by single-crystal X-ray diffraction studies and their spectroscopic (IR, NMR, UV–Vis and fluorescence) properties are described. The structural analyses reveal that compounds 4–9a are centrosymmetric binuclear compounds while compounds 9b (a polymorph of the binuclear compound 9a) and 10 are mononuclear compounds. The HgCl2 compounds are more likely to dimerize via Hg⋯Cl bridges complexed with (E)-N-(pyridin-2-ylmethylidene)arylamine ligands compared with their HgBr2 and HgI2 analogs. This feature of the structural chemistry is correlated with the enhanced Lewis acidity of the mercury in the HgCl2 compounds. Moderating the electronegativity of the substituents in L is shown to influence the strength of the Hg–N(imino) bond in HgCl2L compounds.

Graphical abstractHgX2L molecules invariably dimerize when X = Cl but this tendency decreases for X = Br and I. For the HgCl2L structures, the strength of the Hg–N(imino) bond can be diminished by increasing the electronegativity of the substituents in L.Figure optionsDownload full-size imageDownload as PowerPoint slide