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

Two zinc supramolecular isomers, formulated as alpha-[Zn(cis-cppca)(H2O)](n) (1) and beta-[Zn(trans-cppca)(H2O)](n) (2), have been synthesized under solvothermal conditions and fully characterized (H(2)cppca = 5-(3carboxy- phenyl)-pyridine-2-carboxylic acid). Solvent-induced conformational isomerism of cppca(2-) 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 (A) over circle and the external edge is a circular channel with an approximate dimension of 19.26 (A) over circle. 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.