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International audience; Two organic–inorganic hybrid salts, (C6H9N2)2[Co(C2O4)2]·H2O (1) and (C5H7N2)2[Co(C2O4)2(H2O)2] (2) (C6H9N2+ = 2-amino-3-methylpyridinium; C5H7N2+ = 4-aminopyridinium) have been obtained. Salt 1 is characterized by the formation of one-dimensional chains of the anionic complexes [Co(C2O4)2]2-, with the Co(II) centers located in a distorted (2 + 2 + 2) octahedral environment of six oxygen atoms from three chelating oxalato(2 − ) ligands. By contrast, salt 2 features discrete anionic complexes [Co(C2O4)2(H2O)2]2- with distorted (4 + 2) octahedral CoO6 coordination sphere formed by two bidentate O,O-donor oxalato(2 − ) ligands in the equatorial plane and two aqua ligands in the axial positions. Hydrogen bonding interactions of the type Osingle bondH∙∙∙O and Nsingle bondH∙∙∙O along with π–π stacking interactions between pyridine rings contribute to the stabilization of the 3-D supramolecular frameworks in 1 and 2. Temperature-dependence magnetic moment (µ) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed strong antiferromagnetic ordering below TN = 25 K for 1, a behavior which is confirmed by the negative Weiss constant, θ = − 27.6 K. By contrast, in 2, the Weiss constant, θ = 0 K is in line with a paramagnetic behavior. The three-dimensional Hirshfeld surface (3D-HS) analysis and the two-dimensional fingerprint plots (2D-FP) revealed that in 2, the structure is dominated by H∙∙∙O/ H∙∙∙O and H∙∙∙H contacts.

Two novel bis(oxalato)cuprate(II) salts, (C7H11N2)2[Cu(C2O4)2]·H2C2O4 (1) and (C5H7N2)2[Cu(C2O4)2(H2O)2]·2H2C2O4 (2) {(C7H11N2)+ = 4-dimethylaminopyridinium, (C5H7N2)+ = 3-aminopyridinium} have been synthesized and characterized by elemental and thermal analyses, single-crystal X-ray diffraction, IR spectroscopy and SQUID magnetometry. Compounds 1 and 2 crystallize in the triclinic P-1 space group. The two structures differ in terms of the coordination ligands around the Cu(II) centers as well as the number of the lattice oxalic acid molecules. The crystal structure of 1 is made of columnar stacks of [Cu(C2O4)2]2- anions through axial Cu∙∙∙O contacts (2.89 A), yielding straight Cu(II) chains with a prolate CuO6 octahedron around Cu(II) ions. In this chain structure, the intermetallic Cu∙∙∙Cu separation between two adjacent Cu(II) ions is 3.71 A. The crystal structure of 2 is characterized by the [Cu(C2O4)2(H2O)2]2- complex anion in which aqua ligands are in trans-configuration, with the Cu(II) ion adopting a distorted (4 + 2) octahedral coordination. In the two compounds, the ionic components together with the lattice oxalic acid molecules are connected via intermolecular N H∙∙∙O and O H∙∙∙O hydrogen bonds into a three-dimensional network. In addition, π–π stacking interactions between pyridine rings contribute to the stabilization of the crystal packing. Temperature-dependence susceptibility measurements investigated in the temperature range 2–300 K revealed weak antiferromagnetic coupling at low temperatures in both compounds.