Theoretical and experimental studies on binding mode of 3,5-pyrazoledicarboxylic acid in its new La(III) complex

A new La(III) complex with 3,5-pyrazoledicarboxylic acid (HPy) was synthesized and characterized with elemental analysis, IR, and Raman spectroscopies. Significant differences in the IR and Raman spectra of the complex were observed as compared to the spectra of the ligand. The metal-ligand binding mode was studied on the basis of theoretical and experimental data. B3PW91 and B3LYP methods with 6-311++G∗∗ and LANL2DZ basis sets were successfully applied to study the molecular and vibrational structures as well as the conformational behavior of the neutral ligand and its new La(III) complex. The theoretical calculations of HPy suggested bidentate binding mode through the carboxylic oxygens. Detailed vibrational analysis of HPy and La(III)-Py systems based on both the calculated and experimental spectra confirmed the suggested metal-ligand binding mode. The density functional theory (DFT) calculated geometries, harmonic vibrational wavenumbers including IR and Raman scattering activities for the ligand and its La(III) complex were in good agreement with the experimental data, a complete vibrational assignment being proposed.