Synthesis, characterization and emission study of zinc(II) and cobalt(II) complexes: Bis(bidentate) iminophenols as zinc(II) selective fluorescence probes

Two zinc(II) complexes, [ZnII2(L1)2] (1) and [ZnII2(L2)2] (2), and two cobalt(II) complexes, [CoII2(L1)2] (3) and [CoII2(L2)2] (4), (H2L1 = iminophenol derived from the condensation of 4-aminobenzylamine and salicyldehyde, H2L2 = Schiff-base of 4-aminobenzylamine and 3,5-di-tert-butylsalicyldehyde) supported by bis(N,O-bidentate) ligands have been synthesized and characterized. X-ray single crystal structures of 3 and 4 revealed the dimeric nature of the complexes with a 1:1 ratio of metal and ligand. The zinc(II) complexes have a very similar composition as established from different analytical and spectroscopic techniques. The iminophenols exhibit highly selective fluorescence enhancement with high quantum yield upon binding with Zn2+ in solution. A 50-fold enhancement of emission in zinc(II) complexes is observed with respect to free iminophenols.