Metal-directed assembly of metal(II) benzoates (M = Mn, Ni, Co, Cu, Zn, and Cd) with 1,2-bis(4-pyridyl)ethene: Light- and photo-induced [2 + 2] cycloaddition

We showed a systematic investigation on the coordination polymers assembled from metal(II) benzoates and bpe ligands. 1-Mn and 5-Zn show ladder-type double chains, 2-Co does a simple linear chain, 3-Ni does a two-dimensional sheet, 4-Cu does a chain containing paddle-wheel dinuclear units, 6-Cd does a thick one-dimensional structure containing newly generated [2 + 2] addition product 4pycb ligands. In addition, light-induced [2 + 2] addition reaction occurs for CdII ions, and C = C double bonds that were aligned for photo-induced [2 + 2] cycloaddition in ZnII ion undergo the photo-induced cycloaddition by UV lamp. Luminescences of compounds 3 and 4 showed strong emissions, while relatively weak luminescences were observed for 1 and 2. Moreover, 4-Cu and 1-Mn have shown efficient catalytic reactivities, while 2-Co, 3-Ni and 6-Cd have displayed a very slow conversion. The reactivities of the compounds used in this study are in the order of 5-Zn > 4-Cu > 1-Mn > 2-Co ≫ 3-Ni > 6-Cd.