Synthesis, luminescence and NMR studies of lanthanide (III) complexes with hexafluoroacetylacetone and phenanthroline. Part II

The paper reports the syntheses, 1H NMR spectral and luminescence spectral studies of eight-coordinate Sm, Eu, Tb, Dy and Tm complexes of the type [Ln(hfaa)3(phen)] (hfaa = hexafluoropentanedione and phen = 1,10-phenanthroline). These complexes have been synthesized in high yields by modifying a method reported in literature for synthesizing similar complexes. Large up field and downfield shifts were observed in their 1H NMR spectra. The lanthanide induced chemical shifts in these paramagnetic complexes are dipolar in nature. The H(2) and H(4) proton resonances of phen of the thulium complex have been shifted to highfields which is unusual. Inter- and intra-molecular chemical shift ratios are similar for Sm and Eu complexes as these are isostructural in solution. The quantum yields (Φ = 46% for Eu, 32% for Tb, 2.7% for Sm and 2.1% for Dy) of the complexes indicate that energy transfer from ligands (hfaa and phen) to Ln(III) is efficient. The luminescence in the Dy(III) complex is the least intense due to poor intramolecular energy transfer match as compared to rest of the complexes. The lanthanide ions in these complexes have low symmetry sites.