Construction of Cd(II) compounds with a chelating ligand 2,2′-dipyridiylamine (Hdpa): Anion effect, catalytic activities and luminescence

Six new structures of Cd(II) complexes containing Hdpa ligands have been determined. With chloride and bromide, Cd(II) ions produce halide-bridged dinuclear units 1 and 2 while CdI₂ produces mononuclear unit 3 without halide-bridging. Cd(II) ions produce mono-Hdpa complex 4 with chelating benzoate, di-Hdpa complex 5 with coordinating NO₃^- anion, and tri-Hdpa complexes 6 and 7 with non-coordinating ClO₄^- and BF₄^- anions. One-, two-, or three-dimensional structures of Cd(II)-Hdpa complexes can be produced by hydrogen bonding interactions and π-π interactions. The compounds 4, 5, and 6 catalyzed efficiently the transesterification of a variety of esters with methanol, while 1, 2, 3 and 7 have displayed a very slow conversion. The transesterification reactivity shown by the catalyst 6 is very efficient and the best among the compounds 1-7. In addition, all compounds 1-7 and ligand (Hdpa) have shown the similar luminescent properties at λ_max = 352 nm which suggest that their emissions seem to be attributed to the π-π* intraligand fluorescence.