Three β-octamolybdate-based supramolecular hybrids constructed from a bis-imidazolyl-bis-amide ligand: fast and selective adsorption activities of organic dyes

Abstract

Three β-octamolybdate-based supramolecular hybrids assembled from a semi-rigid bis-imidazolyl-bis-amide ligand, [ML(β-Mo₈O₂₆)_0.5(H₂O)]·H₂O [M = Co (1) and Zn (2)] and [Cu₂L₂(H₂O)](β-Mo₈O₂₆)·4H₂O (3) [L = 1,2-bis(1H-imidazole-4-carboxamido)hexamethylene], have been hydrothermally synthesized, and characterized by FT-IR spectrometry, powder X-ray diffraction (PXRD), thermogravimetric (TG) analyses, and single-crystal X-ray diffraction. Compounds 1 and 2 are isostructural, in which the circular units [M₂L₂]⁴⁺ are linked by [β-Mo₈O₂₆]⁴⁻ polyoxoanions to give a 1D chain, which is further extended into a 3D supramolecular structure through hydrogen bonds. A kind of 1D wave-like chain [Cu₂L₂(H₂O)]⁴⁺ is linked by [β-Mo₈O₂₆]⁴⁻ polyoxoanions via hydrogen bonds, constructing a 3D supramolecular structure in compound 3. The adsorption behaviours of compounds 2 and 3 for organic dyes were investigated in detail. The results indicate that 2 and 3 show fast and selective adsorption and desorption activities for Congo red, as well as excellent stability and recyclability after ten cycles.