Three layer-structured cadmium coordination polymers based on flexible 5-(4-pyridyl)-methoxylisophthalic acid: rapid synthesis and luminescence sensing

Abstract

Based on flexible 5-(4-pyridyl)-methoxylisophthalic acid ligand (H₂L), three layered cadmium coordination polymers, namely [CdL(H₂O)]·2H₂O (1), [CdL(H₂O)(4,4′-bipy)_0.5]·H₂O (2) (4,4′-bipy = 4,4′-bipyridine), and [CdL(H₂O)₂]·0.5H₂bdc (3) (H₂bdc = 1,4-benzene dicarboxylic acid), have been prepared by a rapid microwave (MW)-assisted solvothermal synthesis method. It is noteworthy that the MW-assisted method can effectively accelerate the reaction rate compared with a conventional solvothermal method. 1 exhibits a 2D layer with the quadrangle windows built from dinuclear [Cd₂N₂O₁₀] SBUs and L²⁻ ligands. 2 shows an interesting two-fold interpenetrated 2D layered structure, in which the 4,4′-bipy ligands link the adjacent sheets constructed from Cd²⁺ cations and L²⁻ ligands to build a double-layered structure with rhombic windows. For 3, the Cd²⁺ ions are linked with L²⁻ ligands to form a 2D layer and free H₂bdc ligands penetrate into the rhombic windows of the adjacent layers. Moreover, the activated samples of 1, 2 and 3 possess excellent luminescence sensing properties for Fe³⁺ ions in aqueous solution with high sensitivity and selectivity, respectively.