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

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 2.825 Å in 1, whereas in 2 two different Cu–O bonds (2.814 Å and 2.701 Å) 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 = 3.582 Å. 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 = 3.430 Å and longer inter-dimer spacing of [Cu⋯Cu]inter = 4.961 Å. 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 2–300 K temperature range revealed weak antiferromagnetic coupling in the two hybrid salts.

Graphical abstractTwo new organic–inorganic hybrid salts, bis(guanidinium) bis(oxalato)cuprate(II), (CN3H6)2[Cu(C2O4)2] (1), and bis(2-aminopyridinium) bis(oxalato)cuprate(II) trihydrate, (C5H7N2)2[Cu(C2O4)2]·3H2O (2) have been synthesized and structurally, spectroscopically and magnetically characterized. SQUID magnetometry reveals different antiferromagnetic interactions in the straight and zigzag chains of Cu(II) in 1 and 2, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide