Introducing a flexible tetracarboxylic acid linker into functional coordination polymers: synthesis, structural traits, and photocatalytic dye degradation

This work describes the application of an unexplored aromatic tetracarboxylate building block, 2,3′,4,4′-diphenyl ether tetracarboxylic acid (H4deta), for the synthesis of manganese(ii) and cadmium(ii) coordination polymers (CPs). Five new products, formulated as [Mn2(μ6-deta)(phen)2]n(1), [Cd2(μ6-deta)(phen)2]n(2), [Mn2(μ6-deta)(2,2′-bipy)2]n(3), [Cd2(μ5-deta)(4,4′-bipy)2(H2O)2]n·2nH2O (4), and [Cd2(μ6-deta)(py)(H2O)2]n(5), were assembled using a hydrothermal protocol from the respective metal(ii) chlorides, H4deta, and different mediators of crystallization, namely 1,10-phenanthroline (phen), 2,2′-bipyridine (2,2′-bipy), 4,4′-bipyridine (4,4′-bipy), or pyridine (py). All the CPs1-5were obtained as stable crystalline products and characterized by conventional solid-state methods (elemental analysis, FTIR, UV-vis, TGA, and PXRD) and single-crystal X-ray diffraction. The structures of1-3feature decorated honeycomb-like 2D double layers of a 3,6L66 topological type. Compound4reveals a trinodal 4,4,5-connected 3D metal-organic framework (MOF) with a unique topology, while the 2D coordination polymer5discloses a binodal 4,6-connected layer with a 4,6L45 topology. The structural and topological traits, thermal stability, luminescence properties and photocatalytic activity toward methylene blue degradation were studied for the obtained compounds. In particular, MOF4acts as an active, stable, and recyclable photocatalyst for the UV-light-assisted discoloration of methylene blue in water under ambient conditions. By introducing a novel type of flexible tetracarboxylic acid linker, the present study discloses the first manganese and cadmium compounds derived from H4deta as an unexplored polycarboxylate building block, thus contributing to intensive research on functional metal-organic architectures. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2020.