Two unique cobalt-organic frameworks based on substituted imidazole-dicarboxylate and dipyridyl-type ancillary ligands: Crystal structures and magnetic properties

Two three dimensional (3D) Co(II) coordination polymers incorporating similar substituted imidazole-dicarboxylate and dipyridyl-type ancillary ligands pillared layer, namely, {Co3(mimda3 −)2 (bpe)3·3H2O}n (1) and {Co3 (eimda3 −)2(bipy)3·8H2O}n (2) (H3mimda = 1H-2-methyl-4,5-imidazole-dicarboxylic acid, while H3eimda = 1H-2-ethyl-4,5-imidazole-dicarboxylic acid, bpe = 1,2-di(4-pyridyl) ethylene and bipy = 4, 4′-bipyridine) have been successfully synthesized. Both polymers 1 and 2 have been characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis (TGA). X-ray structural analysis reveals that they are nearly isostructural, possessing similar symmetry units based on trinuclear clusters, and further is propagated into a Kagome-like lattice. The lattice consists of corner-sharing triangles of spins with magnetic coupling between the nearest neighboring Co(II) ions. Magnetic measurements revealed spin-canting-like antiferromagnetism behaviors for compounds 1 and 2 at lower temperature. The interaction in 1 is slightly stronger than that of 2, which can be explained by the discrepancy of organic linker between the adjacent Co(II) centers.