Effect of dicarboxylates with different rigidity and length on crystal structures of cobalt(II) complexes derived from a semi-rigid tri-pyridyl-bis-amide ligand

Four new cobalt(II)-based metal–organic coordination polymers, namely {Co(L)(ox)]·3H₂O}_n (1), Co₂(L)(chda)₂]_n (2), {Co(L)(mip)(H₂O)]·H₂O}_n (3) and Co(L)(oba)]_n (4), L = N,N′-bis(pyridine-3-yl)pyridine-3,5-dicarboxamide, H₂ox = oxalic acid, H₂chda = trans-1,4-cyclohexanedicarboxylic acid, H₂mip = 5-methylisophthalic acid, H₂oba = 4,4′-oxybis(benzoic acid)] were hydrothermally synthesized and structurally characterized by IR, TG, PXRD and single-crystal X-ray diffraction. In 1, the oxalate anions display μ ₂-bridging mode connecting the adjacent 1D Co–L]_n zigzag chains to afford a 2D layer. In 2, the chda anions take the μ ₄-bridging mode connecting the neighboring four Co^II ions to construct a Co–chda]_2n 1D double chain, which contains the Co₂(CO₂)₄ paddle-wheel subunit. These double chains are further linked by L ligands to furnish a 2D layer. In 3–4, Co(II) ions are linked by L ligands to give rise to a 1D left-, right-helical chain Co–L]_n, respectively. These helical chains are further linked by μ ₂-bridging mip and oba anions to furnish a 2D network, respectively. The Co(II) ions, L ligands and dicarboxylates exhibit different coordination modes and conformations. The effect of organic dicarboxylates with different rigidity and length on the structures of the Co(II) complexes is discussed. The fluorescence, electrochemical behaviors and photocatalytic activities of the title complexes are reported.