Three multifunctional three-dimensional metal–organic frameworks based on a flexible N,N′-bis(3-pyridinecarboxamide)-1,6-hexane and 3-nitrophthalate: Syntheses, structures and properties

Three multifunctional three-dimensional (3D) metal–organic frameworks (MOFs) based on the 3-nitrophthalic acid (3-H2NPH) and a flexible bis-pyridyl-bis-amide N,N′-bis(3-pyridinecarboxamide)-1,6-hexane (3-dpyh), namely, [Cu(3-dpyh)(3-NPH)(H2O)2] (1), [Ni(3-dpyh)(3-NPH)(H2O)2] (2), [Co(3-dpyh)(3-NPH)(H2O)2] (3), have been hydrothermally synthesized and structurally characterized. X-ray diffraction analyses reveal that the title complexes are isostructural 3D frameworks. In complexes 1–3, the 3-dpyh shows a μ2-bridging mode to link the adjacent metal ions, forming [M(II)-3-dpyh]n meso-helical chains (M = Cu/Ni/Co). Two carboxyl groups of the 3-NPH anion connect the adjacent metal ions with a μ1-η1:η0 mode to form [M(II)-3-NPH]n meso-helical chains, which further connect with the [M(II)-3-dpyh]n chains, constructing 3D frameworks with CdSO4-like topology. The fluorescent, electrochemical, and photocatalytic properties of complexes 1–3 have also been investigated.