Synthesis, crystal structures and NIR luminescence properties of binuclear lanthanide Schiff Base complexes

Three binuclear lanthanide complexes [Nc(2)(L-1)(3)(MeOH)]center dot MeOH center dot H2O (1) and [Ln(2)(H2L2)(2)(-OAc)(4)]center dot 2 (CF3SO3)center dot MeOH center dot EtOH (Ln = Nd (2) and Ho (3)) were prepared using two Schiff base ligands. Interestingly, 1 has a triple-decker structure with two lanthanide ions enclosed by three rigid conjugated Schiff base ligands (H2L1), while 2 and 3 show nanoscale ring structures (8 x 12 x 12 angstrom) formed by flexible long-chain Schiff base ligands (H2L2, similar to 23 angstrom) with the lanthanide ions located in the center. Upon excitation of the ligand-centered absorption bands, 1-2 and 3 show typical NIR emission spectra for Nd3+ and Ho3+ ions, respectively. In 1, the Nd(III) centers are shielded within the decker-like structure and surrounded by chromogenic Schiff base ligands (energy transfer donors). Luminescence studies show that the NIR emission lifetime of 1 is longer than that of 2 in solution. (C) 2017 Elsevier B.V. All rights reserved.