Syntheses, structures, and luminescent properties of Zn(II) and Cd(II) complexes: 3-D supramolecules based on 2,6-bis(imino)pyridine ligands constructed by hydrogen bonding interactions

Six 5-coordinate 2,6-bis(imino)pyridine metal complexes, [2,6-(ArN=CMe)2C5H3NMCl2 · nCH3CN] (Ar = 4-MeC6H4, M = Zn, n = 0.5, Zn1, M = Cd, n = 1, Cd1; Ar = 2,6-Et2C6H3, M = Zn, n = 0.5, Zn2, M = Cd, n = 0.5, Cd2; Ar = 2,4,6-Me3C6H2, M = Zn, n = 1, Zn3, M = Cd, n = 1, Cd3), were synthesized in acetonitrile by the reactions of the corresponding bis(imino)pyridines with ZnCl2 or CdCl2 · 2.5H2O, respectively. The structures of Zn1–Zn3 and Cd1–Cd3 were determined by the single-crystal X-ray diffraction. In all complexes, the ligand is tridentate with further coordination by two chlorides, resulting in a distorted trigonal bipyramid. All complexes self-assemble through hydrogen bonding interactions to form a 3-D supramolecular structure. At 298 K in dichloromethane, all complexes have blue luminescent emissions at 405–465 nm, which can be attributed to ligand-centered π* → π transitions. The zinc and cadmium centers play a key role in enhancing fluorescent emission of the ligands.