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

Abstract

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-H2DB­TPA), 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]·2H2O (1), {[Cd­(NO3)­(tpeb)­(4-IBA)]·H2O} n (2), {[Cd2­(NO3)2­(tpeb)2­(1,4-BDC)]} n (3), {[Cd2­(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 [Cd2­(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.

Water-Stable Zn(II) Coordination Polymers Regulated by Polysubstituted Benzenes and Their Photocatalytic Performance toward Methylene Blue Degradation Dominated by Ligand-Field Effects

“…The Zn–O and Zn–N bond lengths are comparable to those for the classical Zn­(II) complexes functionalized by carboxylate and/or pyridyl substituents (2.0044–2.1664 Å, Table S1). − The tpt ligand is neutral, affording two exterior N pyridyl donors in a bidentate μ 2 -N,N-bridging fashion. Instead, the HL 1 2– anion is doubly deprotonated, exhibiting a μ 3 -κ 3 O1:O2:O3 manner through two deprotonated carboxylate groups (Figure S3).…”

“…The Zn–O and Zn–N bond lengths are comparable to those of 1 and other known Zn­(II) complexes (Table S2). − The coexistence of the three coordination polyhedra is expected to well-tune the band structure through the type of the donor and their spatial position. Apart from the bidentate bridging mode, the tpt in 2 also takes a terminally unidentate pattern to achieve the metal coordination sphere.…”

“…All the Zn–O and Zn–N bond lengths are comparable to those in Zn­(II)-CPs with carboxylate and pyridyl ligands (Table S3). − The different energy level splits for the d orbitals of the Zn­(II) ion by the specific ligand field can interact with the p orbitals of the donor atoms, effectively tuning the band gaps and the band potentials. Both L 2 3– anions in 3 are completely deprotonated in the identical μ 4 -κ 4 O1:O3:O5:O6-binding mode (Figure S3).…”

“…The internuclear separations of Zn–O and Zn–N are comparable to those of the known Zn­(II)-CPs (Table S4). − The O-containing auxiliary ligand exhibits a hexadentate μ 4 -κ 6 O1:O2,O3:O1′:O2′,O3′ fashion for L 3 4– and a tetradentate μ 4 -κ 4 O1:O2:O1′:O2′ manner for the H 2 L 3 2– anion (Figure S3).…”

“…The Zn–O and Zn–N bond lengths are comparable to those of the known Zn­(II)-CPs (Table S5). − The fully deprotonated L 4 4– ligand affords one sulfonate and three carboxylate segments to bind with the Zn­(II) ion through a μ 5 -κ 7 O1,O9:O2:O3:O4,O5:O5 mode (Figure S3).…”