Solvent-induced construction of two zinc supramolecular isomers: synthesis, framework flexibility, sensing properties, and adsorption of dye molecules

Abstract

Two zinc supramolecular isomers, formulated as α-[Zn(cis-cppca)(H₂O)]_n (1) and β-[Zn(trans-cppca)(H₂O)]_n (2), have been synthesized under solvothermal conditions and fully characterized (H₂cppca = 5-(3-carboxy-phenyl)-pyridine-2-carboxylic acid). Solvent-induced conformational isomerism of cppca²⁻ ligand and framework isomerism of 1 and 2 are both observed. Each distorted [Zn(cis-cppca)]₂ unit joined four equivalent ones in an abnormal 2D puckered layer in compound 1; however, compound 2 displays a 3-D open framework with larger bi-edge channels constructed by 1D Zn–O–Zn chains and trans-cppca bridges, in which the internal edge is a nearly hexagonal channel with an approximate dimension of 14.51 Å and the external edge is a circular channel with an approximate dimension of 19.26 Å. Fluorescent properties indicated that compound 1 displays an apparent fluorescence emission in acetone solvent; however, compound 2 was very sensitive to acetone molecules which results in nearly 100% fluorescence quenching. Moreover, compounds 1 and 2 might be promising luminescent probes for the detection of Fe³⁺. The dye adsorption experiments demonstrated that compound 2 showed good adsorption properties for MB and RhB molecules.