1H NMR of paramagnetic Lanthanide(III) complexes of trifluoroacetylacetone and 2,2′-Bipyridyl and 4f-4f absorption studies

Abstract

A series of anhydrous eight-coordinate air and moisture stable lanthanide (III) complexes of 1,1,1-trifluoro-2,4-pentanedione (tfaa) and 2,2′-bipyridyl (bpy) of the type [Ln(tfaa)3(bpy)] [Ln = La (1), Nd (2), Ho (3), Er (4), Yb (5) and Lu (6)] have been synthesized in high yield by a one-step method and characterized by elemental analyses, ESI-MS+, TGA, DTA IR and 1H NMR spectroscopy. The NMR spectra of diamagnetic and paramagnetic complexes reveal that the bpy unit remains attached to the metal in solution. The β-diketonate (methine and methyl) and bpy protons resonances are shifted in opposite directions in a given paramagnetic complex and the lanthanide-induced shifts are dipolar in nature. The 4f - 4f absorption spectra of the complexes of Nd(III), Er(III) and Ho(III) are analyzed. The hypersensitive transitions of Nd(III), Er(III) and Ho(III) complexes are sensitive to the environment (ligand/solvent), which is reflected by different oscillator strengths and distinctively different band shapes of the hypersensitive transitions. The coordination geometries of [Ln(tfaa)3H2O] and [Ln(tfaa)3(bpy)] (Ln = La and Nd) are calculated using the Sparkle/PM3 model.