A polymeric Co(II) oxalate salt containing pyridinium type cations: Synthesis, structure, spectroscopy, thermal behavior and magnetism

A Co(II) oxalate coordination polymer, (C7H11N2)(2)[Co(C2O4)(2)]center dot 5H(2)O (1) (C7H11N2+ = 2-amino-4,6-dimethylpyridinium cation), has been synthesized and characterized by elemental and thermal analyses, FT-IR and UV/Vis spectroscopies, powder X-ray diffraction (PXRD), single-crystal X-ray diffraction and variable temperature magnetic susceptibility measurements. Compound 1 is a polymerized organic-inorganic hybrid salt, the asymmetric unit of which consists of one Co(II) ion, one bidentate C2O42- ligand, two halves of bidentate C2O42- ligands, two 2-amino-4,6-dimethylpyridinium C7H11N2+ cations and five crystal water molecules. Each CoII center is six-coordinated in a distorted octahedral geometry fulfilled by six oxygen atoms from three chelating C2O42- ligands. The [Co(C2O4)(2)](2-) ions act as complex ligands and efficiently bridge neighboring Co2+ ions, forming chains of complex anions linked by hydrogen bonded water molecules. Hydrogen bonding interactions of the type O-H center dot center dot center dot O and N-H center dot center dot center dot O along with pi-pi stacking interactions between pyridine rings contribute to the stabilization of the 3D supramolecular framework. Temperature-dependence magnetic moment (mu) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed weak antiferromagnetic ordering at low temperatures.