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

Abstract 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 [HgX 2 L] 2 : X = Cl; R = 4-CH 2 CH 3 ( 4 ), 4-OCH 2 CH 3 ( 5 ), 4-Cl ( 6 ), 2-CO 2 CH 3 ( 7 ), or 4-CO 2 CH 3 ( 8 ); X = Br; R = 4-CO 2 CH 3 ( 9a ) and [HgX 2 L]: X = Br; R = 4-CO 2 CH 3 ( 9b ) and X = I; R = 4-CO 2 CH 3 ( 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 HgCl 2 compounds are more likely to dimerize via Hg⋯Cl bridges complexed with ( E )- N -(pyridin-2-ylmethylidene)arylamine ligands compared with their HgBr 2 and HgI 2 analogs. This feature of the structural chemistry is correlated with the enhanced Lewis acidity of the mercury in the HgCl 2 compounds. Moderating the electronegativity of the substituents in L is shown to influence the strength of the Hg–N(imino) bond in HgCl 2 L compounds.