Raman, FT-IR, and DFT studies of 3,5-pyrazoledicarboxylic acid and its Ce(III) and Nd(III) complexes

3,5-Pyrazoledicarboxylic acid was used as a ligand for the synthesis of its Ce(III) and Nd(III) complexes. The complexes of Ce(Ill) and Nd(III) with 3,5-pyrazoledicarboxylic acid were synthesized and their compositions were determined by elemental analysis. Vibrational study in the solid state of 3,5-pyrazoledicarboxylic acid and its new Ce(III) and Nd(III) complexes was performed by IR and Raman spectroscopy. The changes observed between the IR and Raman spectra of the ligand and of the complexes allowed us to establish the coordination mode of the metal in both complexes. The comparative vibrational analysis of the free ligand and its lanthanide(III) complexes gave evidence that 3,5-pyrazoledicarboxylic acid binds Ln(III) through the deprotonated carboxylic oxygens. The density functional theory (DFT) calculated geometries, harmonic vibrational modes and Raman scattering activities of the ligand were in good agreement with the experimental data, and a complete vibrational assignment is being proposed. The experimental IR and Raman bands of the ligand were assigned to normal modes on the basis of IDFT calculations. The effect of the intramolecular hydrogen bonds in the ligand on vibrational mode positions is also discussed. The characteristic IR and Raman bands of 3,5-pyrazoledicarboxylic acid and its lanthanide complexes were specified and discussed. Copyright (c) 2006 John Wiley & Sons, Ltd.