Hydrogen-bonded 3D network of d10-metal halide coordination polymer containing N-(3-pyridinyl) nicotinamide: influence of ligand conformation, halide anions and solvent

Abstract

In this study, four new d¹⁰-metal halide coordination polymers (CPs), namely [HgCl₂ (3-pna)]_n (1), [HgBr₂(3-pna)]_n (2), [HgI₂(3-pna)]_n CH₃OH (3) and [CdI₂(3-pna)]_n (4), (3-pna = N-(3-pyridinyl)nicotinamide) were prepared through the reaction of mercury(II) or cadmium(II) salts with 3-pna by a solution-based method and structurally characterized via single-crystal X-ray diffraction. Moreover, X-ray crystal structure determination of 3-pna is reported for the first time. From the viewpoint of green chemistry, solid state reactivity of the starting materials of compounds 1 and 2 was investigated by mechanochemical and thermal synthesis methods under solvent-free conditions. Powder X-ray diffraction (PXRD) patterns of the reaction mixture upon grinding of the starting reactant and powders isolated from heating the reactant materials were successfully matched with simulated PXRD patterns of the compounds. According to single-crystal X-ray analysis, all compounds 1–4 are isostructural CPs as one-dimensional (1D) zigzag chains based on the anti conformation of the ligand. The accompanying halogen ions are observed to form C/N–H⋯X (X = Cl, Br, I) hydrogen bonds resulting in 3D supramolecular architectures. The presence of solvent molecules in the mercury iodide complex expands the packing structure with the change of halogen-based interactions to N–H⋯O_solvent and C–H⋯O_amide interactions. Conformational dependence of ligand interactions was investigated on the reported 3-pna complexes in the Cambridge Structural Database (CSD). The results revealed that supramolecular synthons of the amide skeleton of the ligand as well as the polymeric architecture of the complex are significantly influenced by the anti/syn conformation of the ligand.