Thermal Cleavage of Cyclobutane Rings in Photodimerized Coordination-Polymeric Sheets

摘要: Three coordination polymers, [Cd(2)(pvba)(2)(tbdc)(dmf)(2)] (1), [Co(2)(pvba)(2)(tbdc)(dmf)(2)(H(2)O)(2)] (2), and [Ni(2)(pvba)(2)(tbdc)(dmf)(2)(H(2)O)(2)] (3) (H(2)tbdc = 2,3,5,6-tetrabromobenzenedicarboxylic acid, Hpvba trans-2-(4'-pyridyl)vinylbenzoic acid), were synthesized by solvothermal methods. The solid-state structures of compounds 1 2 determined X-ray crystallography. In 2, the bimetallic cores acted as secondary building units that connected tbdc ligands in one direction a pair pvba ligands, which aligned head-to-tail parallel manner, orthogonal to form sheet structures. C=C bonds these ligand pairs all three well-aligned undergo quantitative [2+2] cycloaddition reactions solid state under UV irradiation, thereby yielding their cyclobutane derivatives. This photochemical reaction appeared facilitate structural transformations from 2D structure into another state. photoreactive Co(II)- Ni(II) polymers exhibited reversible dehydration-rehydration was accompanied color changes pink purple green yellow, respectively, owing change number six five. Magnetic studies showed compound an antiferromagnet, displayed field-dependent transition with critical field (H(c)) 40 kOe at K; antiferromagnetic interaction between Co(2) strengthened weakened dehydration respectively. photodimerized products cleaved on heating yield mixture trans- cis-isomers pvba, monitored (1)H NMR spectroscopy. Cd(II) polymer underwent cleavage ring whilst other two partial cleavage.