Structural properties and thermal decomposition of three heteroleptic coordination polymers with oxalate, 2-aminomethylpyridine and metal = Zn2+, Ni2+ and Cu2+

Three heteroleptic one-dimensional (1D) (2-aminomethylpyridine-κ²N,N′)(μ-oxalato-κ²O,O'':κ²O',O‴) metal coordination polymers 1D-[Zn(ampy)(μ-ox)]·H₂O (1), 1D-[Ni(ampy)(μ-ox)]·H₂O (2) and 1D-[Cu(ampy)(μ-ox)H₂O] (3) were synthesized and the product of their calcination was investigated. Compounds 1 and 2 are new and isomorphous. In their packing, the metal-oxalate units build zigzag chains along the a direction through the bisbidentate chelating and bridging coordination mode of oxalate. These chains build supramolecular layers in the ab plane through C–H···π interactions between the aminomethylpyridine ligands. The layers are connected with water molecules to form bilayers that run along the c-axis. The thermal decomposition process of the three materials in the air is complete at around 500 °C and yields ZnO, NiO, and CuO respectively while under N₂, the decomposition mechanism is different and produces around 600 °C, ZnO, Ni, and Cu respectively. Further decomposition of this ZnO in this oxygen-free atmosphere is observed at 800 °C and the remaining material shows a smaller average apparent crystallite size and is more dispersed than the ZnO obtained in air where such mass loss is not observed. However, both ZnO show the same quantity of defects. This work shows the importance of the atomic absorption spectroscopy measurements of oxide materials that would have defects.