Solution studies of lanthanide (III) complexes based on 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and 1,10-phenanthroline Part-I: Synthesis, 1H NMR, 4f–4f absorption and photoluminescence

Solution studies on the complexes of the type [Ln(hfaa)3(phen)2] (Ln = La, Pr and Nd) and [Ln(hfaa)3phen] (Ln = Nd, Ho, Er and Yb; hfaa stands for the anion of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione and phen stands for 1,10-phenanthroline) are presented. These complexes are synthesized in high yields by an in situ method in which hfaa, ammonium hydroxide, lanthanide chlorides and phen were allowed to react in 3:3:1:1 molar ratio in ethanol. In the case of neodymium both eight- and ten-coordinate complexes are isolated. The paramagnetic shifts of the methine protons of β-diketone have their sign opposed to those of paramagnetic shifts of phen protons and the shifts are dominated by dipolar interactions. The inter- and intramolecular shift ratios have been calculated and discussed. The 4f–4f absorption spectra of the complexes of Pr, Nd, Ho and Er are analyzed. The eight- and ten-coordinate neodymium complexes display distinctively different band shapes of the 4G5/2,2G7/2 ← 4I9/2 hypersensitive transition. The efficient energy transfer from ligand to Pr(III) is reflected by strong red luminescence of this complex at room temperature.

Graphical abstractAbsorption, emission and NMR studies on the complexes of the type [Ln(hfaa)3(phen)2] (Ln = La, Pr and Nd) and [Ln(hfaa)3(phen)] (Ln = Nd, Ho, Er, Yb and Lu) are presented. Only neodymium gives both eight- and ten-coordinate complexes. The strong red emission of Pr(III) complex originates from 1D2 level.Figure optionsDownload full-size imageDownload as PowerPoint slide