Thermally Induced Single -Crystal -to-Single-Crystal Transformation and Heterogeneous Catalysts for Epoxidation Reaction of Co(II) Based Metal-Organic Frameworks Containing 1,4-Phenylenediacetic Acid

Four new metal-organic frameworks (MOFs) based on 1,4-phenylenediacetic acid (1,4-H(2)phda), [Co(1,4-phda)(4,4'-bpa)] (1), [Co(1,4-phda)(4,4'-bpp)] (2), [Co (1,4-phda) (4,4'-bpa) (H2O)(2)] (3), and [Co (1,4-phda)(4,4'-bpa)] (3a) (4,4'-bpa = 1,2-bis(4-pyridyl)ethane and 4,4'-bpp = 1,3-bis(4-pyridyl)propane) were successfully synthesized. The various synthetic methods play an important role in the formation of diverse structural frameworks. Compound 1 shows a 3D framework, while 2, 3, and 3a exhibit 2D layered MOFs with different architectures. The irreversible thermally induced single-crystal-to-single-crystal transformation with chromotropism from 3 to 3a was observed, which was established by the breakage and reformation of coordination bonds around Co(II) centers. The orientation of coordinated 4,4'-bpa ligand and conformation of 1,4-phda ligand play a key role on pore opening in 3 and pore closing in 3a. Furthermore, the functional properties as heterogeneous catalysts of these MOFs including epoxidation of alkenes and photocatalytic performance for MB degradation have been investigated. The heterogeneous catalytic properties of 1, 2, and 3a exhibit high catalytic activity with good catalyst stability.