Carboxylate-Assisted Assembly of Zinc and Cadmium Coordination Complexes of 1,3,5-Tri-4-pyridyl-1,2-ethenylbenzene: Structures and Visible Light-Induced Photocatalytic Degradation of Congo Red in Water

Solvothermal reactions of zinc and cadmium nitrates with 1,3,5-tri-4-pyridyl-1,2-ethenylbenzene (tpeb) in the presence of various carboxylic acids including 4-iodobenzoic acid (4-HIBA), benzene-1,4-dicarboxylic acid (1,4-H2BDC), 2,5-furandicarboxylic acid (2,5-H2FDC), 2,5-dibromoterephthalic acid (2,5-H(2)DBTPA), 1,2-cyclohexanedicarboxylic acid (1,2-H2CHDC), and 1,5-pentanedioic acid (1,5-H2PDC) gave rise to eight coordination complexes, viz, [Zn(tpeb)2(4-IBA)(2)]2H(2)O (1), {[Cd(NO3)(tpeb)(4-IBA)]H2O}n (2), {[Cd-2(NO3)(2)(tpeb)2(1,4-BDC)]}n (3), {[Cd-2(tpeb)2(2,5-FDC)(2)]2H2O}n (4), [Cd(tpeb)(2,5-DBTPA)2]n (5), {[Cd2(H2O)2(tpeb)2(1,2-CHDC)2]H2O}n (6), [Zn(tpeb)(1,2-CHDC)]n (7), and {[Zn(tpeb)(1,5-PDC)]H2O}n (8). Compound 1 is a discrete mononuclear complex with its Zn(II) center coordinated by two pairs of tpeb and 4-IBA ligands. Compound 2 has a 2D waterfall-like network constructed from bridging [Cd(NO3)(4-IBA)] units with tpeb ligands. Compounds 3, 4, and 5 contain similar 1D [Cd(tpeb)]n chains, which are linked by 1,4-BDC, 2,5-FDC, and 2,5-DBTPA bridges, respectively, forming either 2D (2 and 3) networks or a 3D (4) framework. Compound 6 holds a 2D wavelike layer structure in which dimeric [Cd-2(H2O)(2)(1,2-CHDC)(2)] fragments are connected by two couples of tpeb ligands. Compounds 7 and 8 contain similar 2D fish-scale networks assembled from 1D chains of [Zn(1,2-CHDC)]n or [Zn(1,5-PDC)]n bridged by tpeb ligands. Compound 6, as a representative sample, has larger absorption in the visible light region, and can be employed to efficiently degrade Congo red in water without additional oxidizing or reducing reagents upon visible light irradiation. This photocatalyst could be recycled at least five times without evident loss of its catalytic efficiency.