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

Abstract

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 CPs 1–5 were 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 of 1–3 feature decorated honeycomb-like 2D double layers of a 3,6L66 topological type. Compound 4 reveals a trinodal 4,4,5-connected 3D metal–organic framework (MOF) with a unique topology, while the 2D coordination polymer 5 discloses 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, MOF 4 acts 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.