(<i>E</i>)-<i>N</i>-(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

Abstract

Using five Schiff base ligands (E)-N-(pyridine-2-yl) (CH═NPhR) (where R = 4–CH3, L1; 2,6-(CH3)2, L2; 2,4,6-(CH3)3, L3; 2,6-(C2H5)2, L4; 2,6-(i-C3H7)2, L5), nine Zn(II)/Cd(II) complexes, namely, Zn1–Zn3, Cd1, Cd2, Cd3a, Cd3b, Cd4, and Cd5, 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 1H 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···O/C–H···Cl hydrogen bonds and π···π 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.