The paramagnetic metal effect on the luminescence of rare-earth-metal complexes with pyridine-based nitrogen ligands

The synthesis and the characterization in the solid state are presented of La(III), Gd(III) and Lu(III) nitrate complexes with the pyridine-based ligands L1 (N,N′-bis(2-pyridylmethylidene)-1,2-(R,R+S,S)-cyclohexanediamine) and L2 (N,N′-bis(2-pyridylmethyl)-1,2-(R,R+S,S)-cyclohexanediamine). The crucial role of the nature of both the lanthanide ion and the ligand in the luminescence spectroscopy of the metal complexes, in the solid state at room temperature, is demonstrated and discussed. In particular, the "paramagnetic effect" of the Gd(III) ion inducing an increased phosphorescence emission is observed in the complex with L1 ligand and, in a lesser extent, in the complex with L2 ligand. At variance with this observation, only fluorescence emission of the La(III) and Lu(III) diamagnetic metal complexes is detected. © 2015 Elsevier B.V. All rights reserved.