Spectroscopic studies of lanthanide picrate complexes with N,N-dimethylacetamide. Structure of the La compound

Abstract

Emission and excitation spectra were recorded for the complexes Ln(pic)3.3(DMA) (pic=picrate, DMA=N,N-dimethylacetamide, Ln=La, Eu, Gd, Sm, Lu). The Eu and Sm complexes exhibit f–f characteristic luminescence spectra, while the other present broad emission bands are due to picrate anion luminescence. Both emission and excitation spectra of the Eu compound point to a small participation of the 5D1 state in the emission process. Lifetimes for these luminescences were measured. Their values (in the range of ms) suggest a strong mixing of the singlet and triplet states of the ligands, as well as a fast transfer to the 5D0 and 4G5/2 states of Eu and Sm, respectively. For the Sm complex doped with Eu, small variations in the lifetimes were observed. Luminescence quantum yields were also determined. Single-crystal X-ray analysis of the La complex shows a D3h symmetry around the central ion.