Heterobinuclear Zn-Ln (Ln = La, Nd, Eu, Gd, Tb, Er and Yb) complexes based on asymmetric Schiff-base ligand: synthesis, characterization and photophysical properties

With a novel asymmetric Schiff-base zinc complex ZnL (H2L=N-(3-methoxysalicylidene)-N'-(5-bromo-3-methoxysalicylidene)phenylene-1,2-diamine), obtained from phenylene-1,2-diamine, 3-methoxysalicylaldehyde and 5-bromo-3-methoxysalicylaldehyde, as the precursor, a series of heterobinuclear Zn-Ln complexes [ZnLnL(NO3)(3)(CH3CN)] (Ln=La, 1; Ln=Nd, 2; Ln=Eu, 3; Ln=Gd, 4; Ln=Tb, 5; Ln=Er, 6; Ln=Yb, 7) were synthesized by the further reaction with Ln(NO3)(3)center dot 6H(2)O, and characterized by Fourier transform-infrared, fast atom bombardment mass spectroscopy and elemental analysis. Photophysical studies of these complexes show that the strong and characteristic near-infrared luminescence of Nd3+, Yb3+ and Er3+ with emissive lifetimes in the microsecond range has been sensitized from the excited state of the asymmetric Schiff-base ligand due to effective intramolecular energy transfer; the other complexes do not show characteristic emission due to the energy gap between the chromophore and lanthanide ions. Copyright (c) 2012 John Wiley & Sons, Ltd.