A mechanistic insight into the rapid and selective removal of Congo Red by an amide functionalised Zn(ii) coordination polymer

Abstract

New CPs [Zn(μ-1κOO′:2κN-L)(H₂O)(BDC)_0.5]_n·n(DMF) (1), [Cd(μ-1κO:2κN-L)₂(H₂O)₂]_n (2), and [Pb(μ-1κOO′:2κO′-L)(μ-1κO:2κO′:3κN-L)]_n (3) [L = 4-(pyridin-3-ylcarbamoyl)benzoate; BDC = benzene-1,4-dicarboxylate] were synthesized and characterized by elemental, FT-IR, powder, and single-crystal X-ray diffraction analyses. Single crystal X-ray diffraction analysis discloses 1D polymeric architectures for 1 and 2 and a 2D one for 3. The topological analysis exemplifies a 2,2,3-connected 3-nodal net with the point symbol {8²·12}₂{8}₃ for 1, a 2,4-connected bimodal net for 2, and a 3,4,7-connected trinodal net for 3. CP 1 shows a selective removal of the Congo Red (CR) dye amongst various dyes. It can be recycled and reused without any significant loss of its dye removal efficiency. An insight into the selective removal of the Congo dye is provided by in silico studies, being accounted for by anion-π, cation-π, and π–π stacking interactions, involving the Zn(II) ion, phenyl rings, and O_carboxylate of L, and the phenyl rings, naphthalene rings, and O_sulfonate of CR.