The Infrared Spectra and Some Properties of Tris-(acetylacetonato) Lanthanide(III) Complexes

Abstract

Abstract The infrared spectra of tris-(acetylacetonato) complexes of praseodymium(III), neodymium-(III), europium(III), gadolinium (III), dysprosium(III), and erbium(III) have been measured in the range between 4000 and 100 cm−1 in order to obtain information about the nature of lanthanide metal-oxygen bond; some properties of these complexes were studied, also. The calculated frequencies and assignments were used to elucidate the complex spectra and to show the relations between the calculated force constants and some physicochemical properties. Although the molecules of each complex were 1 : 3 complexes, the calculation of the vibrational frequencies was made by using a simplified model of the 1 : 1 complex (C2v), because it may be supposed that this tris-(acetylacetonato) complex does not always have a regular octahedral symmetry in spite of the composition of Ln(acac)3. The calculated frequencies were in good agreement with the observed ones; the lanthanide metal-oxygen stretching vibrations were found at 420–432 cm−1 (A1-ν5) and 304–322 cm−1 (B1-ν14). The lanthanide metal-oxygen stretching force constant increases with an increase in the atomic number, while the corresponding C=O stretching frequency (A1-ν1) decreases in the same order. For example, the values of K(Pr–O) and K(Er–O) are 2.10 and 2.29 md/Å respectively. As the result of the lanthanide contraction, the force constant of the lanthanide metal-oxygen bond increases with a decrease in the M–O bond length, thus increasing the stability constant, log β, and slightly increasing the electronegativity.