Preparation and properties of complexes between rare earth trifluoroacetates and hexamethylphosphoramide (HMPA)

Complexes of composition [Ln(TFA)(3)(KMPA)(3)] (Ln=La, Nd, Eu, Gd, Dy, Ho and Er, TFA=trifluoroacetate) were prepared and characterized by complexometric analyses with EDTA and CHN microanalytical procedures. IR spectra show that HMPA's are linked to the central ions through the P=O oxygen and that the trifluoroacetate ions are also coordinated. The visible absorption spectrum of the neodymium compound in a silicone mull, at room temperature, allows us to calculate the nephelauxetic parameter beta=0.990, the covalent factor b(1/2)=0.070 and Sinha's parameter delta=1.01. They are suggestive of an essentially electrostatic interaction between lanthanide and ligands. The emission spectra of the europium complex at room temperature and at 77 K were also determined. Thermogravimetry show that HMPA molecules are totally evaporated at ca. 260 degrees C and that the residues are the corresponding rare earth oxyfluorides. (C) 2000 Elsevier Science S.A. All rights reserved.