Two novel organic–inorganic hybrid compounds with straight and zigzag chain alignments of Cu(II) centers: Synthesis, crystal structure, spectroscopy, thermal analysis and magnetism

Abstract

Two hybrid salts, viz. bis(guanidinium) bis(oxalato)cuprate(II) (1) and bis(2-aminopyridinium) bis(oxalato)cuprate(II) trihydrate (2) have been synthesized and characterized by elemental and thermal analyses, IR spectroscopy, single-crystal X-ray diffraction and SQUID magnetometry. Compounds 1 and 2 crystallize in the monoclinic P21/c and triclinic P1¯ space groups, respectively. In both structures, the four-coordinated Cu(II) ion in [Cu(C2O4)2]2− unit weakly interacts with two axial O-atoms of neighboring units to build a prolate CuO6 octahedron, with regular axial Cu–O bonds of 2.825Å in 1, whereas in 2 two different Cu–O bonds (2.814Å and 2.701Å) are found. In 1, stacking of [Cu(C2O4)2]2− units across internal symmetry-related O-atoms results in equidistantly spaced monomers, thus forming straight Cu(II) chains with regular spacing of Cu⋯Cu=3.582Å. By contrast, in 2, stacking of the [Cu(C2O4)2]2− entities occurs via external symmetry-related O-atoms, yielding zigzag Cu(II) chains with shorter intra-dimer spacing of [Cu⋯Cu]intra=3.430Å and longer inter-dimer spacing of [Cu⋯Cu]inter=4.961Å. The anhydrated compound 1 is stable up to 250°C, whereas the hydrated compound 2 shows a significant weight loss of solvent water molecules at about 70°C, followed by the decomposition of the network. The magnetic measurements in the 2–300K temperature range revealed weak antiferromagnetic coupling in the two hybrid salts.