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]·5H₂O (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 Co^II 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 OH∙∙∙O and NH∙∙∙O along with π–π stacking interactions between pyridine rings contribute to the stabilization of the 3D supramolecular framework. Temperature-dependence magnetic moment (µ) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed weak antiferromagnetic ordering at low temperatures.