(E)-N-(Pyridine-2-ylmethylene)arylamine as an Assembling Ligand for Zn(II)/Cd(II) Complexes: Aryl Substitution and Anion Effects on the Dimensionality and Luminescence Properties of the Supramolecular Metal Organic Frameworks

Using five Schiff base ligands (E)-N-(pyridine-2-yl) (CH=NPhR) (where R = 4-CH3, L-1; 2,6-(CH3)(2), L-2; 2,4,6-(CH3)(3), L-3; 2,6-(C2H5)(2), L-4; 2,6-(i-C3H7)(2), L-5), nine Zn(II)/Cd(II) complexes, namely, Zn1-Zn3, Cd1, Cd2, Cd3a, Cd3b, Cd4, and CdS, have been successfully synthesized. The structures of the Zn(II)/Cd(II) complexes have been established by single crystal X-ray diffraction and further physically characterized by H-1 NMR, FT-IR, and elemental analysis. The crystal structures of these complexes indicate that the structures of ligand and anions can directly influence the formation of 1D -> 3D supramolecular metal-organic frameworks (SMOFs) via C-H center dot center dot center dot O/C-H center dot center dot center dot Cl hydrogen bonds and pi center dot center dot center dot pi interactions. Upon irradiation with UV light, the nine Zn(II)/Cd(II) complexes display deep blue emissions of 401-436 nm in acetonitrile solution and light blue or bluish green emissions of 485-575 nm in the solid state, respectively. The photoluminescence properties of nine Zn(II)/Cd(II) complexes can be finely and predictably tuned over a wide range of wavelengths by small and easily implemented changes to ligand structure. It is worth noting that Zn1 and Cd1 exhibit obvious aggregation-induced emission enhancement (AIEE) properties in the CH3CN-H2O mixture solutions.