Structural, luminescent, and magnetic properties of three novel three-dimensional metal-organic frameworks based on hexadentate N, N-bis(4-picolinoyl)hydrazine

Three novel microporous three-dimensional (3-D) metal-organic framework materials [ML]_n [M = Ni, Co, Cd; L = N, N'-bis(4-picolinoyl) hydrazine] were obtained from hydrothermal reactions. The organic ligand L was formed through the in situ ring-opening hydrolysis reaction of 2,5-bis(4-pyridyl)-1,3,4-oxadiazole with the assistance of metal ions. Single-crystal X-ray diffraction studies reveal that complexes 1-3 adopt 6-connected 3-D networks of distorted a-Po topology, which are built from non-interpenetrated (4,4) grids cross-linked by zigzag chains. These isomorphic complexes are all of high thermal stability, but some other physical properties are quite different because of their different metal centers. Antiferromagnetic exchange was observed between Ni(II) centers of complex 1, while ferromagnetic for Co(II) centers of complex 2. Complex 3 exhibits strong fluorescence emission.