Cadmium(II) Coordination Polymers of 4-Pyr-poly-2-ene and Carboxylates: Construction, Structure, and Photochemical Double [2 + 2] Cycloaddition and Luminescent Sensing of Nitroaromatics and Mercury(II) Ions

Solvothermal reactions of Cd(NO3)2·4H2O with 4-pyr-poly-2-ene (ppene) in the presence of benzene-1,2-dicarboxylic acid (1,2-H2BDC), benzene-1,3-dicarboxylic acid (1,3-H2BDC), benzene-1,4-dicarboxylic acid (1,4-H2BDC), benzene-1,3,5-tricarboxylic acid (1,3,5-H3BTC), or 4,4′-oxidibenzoic acid (4,4′-H2OBA) afforded five Cd(II) coordination polymers [Cd(ppene)(1,2-BDC)]n (1), [Cd(ppene)(1,3-BDC)]n (2), [{Cd(ppene)(1,4-BDC)}·MeCN]n (3) (Liu et al. Inorg. Chem. Commun. 2015, 58, 1−4), [{Cd(ppene)(1,3,5-HBTC)}·0.5(ppene)]n (4), and [Cd(ppene)(4,4′-OBA)]n (5), respectively. Upon UV light irradiation, 1, 3, and 4 can undergo a double [2 + 2] cycloaddition reaction to yield their corresponding photoproducts including [Cd2(4-tp-3-lad)(1,2-BDC)2]n (1a, 4-tp-3-lad = 2,3,5,6-tetra(pyridin-4-yl)bicyclo[2.2.0]hexane), [{Cd2(4-tp-3-lad)(1,4-BDC)2}·2MeCN]n (3a), and [{Cd2(4-tp-3-lad)(1,3,5-HBTC)2}·(ppene)]n (4a) in a single-crystal-to-single-crystal manner. Compounds 1, 2, 4, 5, 1a, 3a, and 4a have been structurally charac...