Various amide derivatives induced Keggin-type SiW12O404−-based cobalt complexes: assembly, structure, electrochemical sensing and dye adsorption properties

Abstract

The self-assembly of different amide derivative ligands, N-(quinoline-5-yl)-1H-imidazole-4-carboxamide (L¹), 4-[(1H-imidazole-4-carboxamide)ethyl]phenyl-1H-imidazole-4-carboxamide (L²) and bis[4-(1H-imidazole-4-carboxamide)phenyl]methanone (L³), with cobalt ions and [SiW₁₂O₄₀]⁴⁻ anion under mixed solvent conditions presented three new Keggin-type polyoxometalate-based metal–organic complexes (MOCs), [Co(HL¹)₂(H₂O)₂][SiW₁₂O₄₀] (1), [Co₂(L²)₂(H₂O)₂(SiW₁₂O₄₀)] (2) and [Co₂(L³)₂(H₂O)₂(SiW₁₂O₄₀)] (3), respectively. MOCs 1–3 displayed novel various two-dimensional supramolecular structures. Complex 1 consists of a mononuclear fragment {Co(L¹)₂} and a [SiW₁₂O₄₀]⁴⁻ anion. Complexes 2 and 3 contain a type of ladder-like chain, which was constructed from a {Co₂L₂(H₂O)₂}⁴⁺ chain as the side rail and [SiW₁₂O₄₀]⁴⁻ anion as the middle rail. The effects of mixed solvent ratio on the formation of MOCs and that of organic ligands on the architectures and properties were discussed. Complexes 1 and 3 not only possess electrocatalytic reduction activity for bromate, nitrite, and Cr(VI) ions, but also show excellent electrochemical sensing behavior for bromate, nitrite, and Cr(VI) ions. In addition, organic dyes such as methylene blue and neutral red could be effectively adsorbed by complexes 1–3.