Synthesis, structures, thermal and magnetic properties of two bis(oxalato)cuprate(II) hybrid salts containing pyridinium derivative cations

Two bis(oxalato)cuprate(II) hybrid salts, (C5H7N2)2[Cu(C2O4)2]·2H2O (1) and (C7H11N2)2[Cu(C2O4)2]·5H2O (2) (C5H7N2 = 3-aminopyridinium; C7H11N2 = 2-amino-4,6- dimethylpyridinium) have been synthesized and characterized by elemental and thermal analyses, IR and UV-Vis spectroscopies, single-crystal X-ray diffraction, and SQUID magnetometry. The polymeric anionic motifs in the two salts are significantly different. In 1, stacking of [Cu(C2O4)2]2- units through axial Cu···O contacts (2.890 Å) yields straight Cu(II) chains, with a prolate CuO6 octahedron around Cu(II) ions, formed by two cis-chelated oxalate anions and two axial O-atoms of neighboring [Cu(C2O4)2]2- units. By contrast, in 2, stacking of [Cu(C2O4)2]2- units occurs via bis-bidentate oxalate groups, yielding zigzag Cu(II) chains with a distorted CuO6 coordination sphere. Thermal studies confirmed the presence of solvent water molecules in both salts. Magnetic studies revealed weak antiferromagnetic and weak ferromagnetic interactions between Cu(II) ions in 1 and 2, respectively