Study of the structures of free nipecotic acid and nipecotamide molecules and their complexes by using vibrational spectroscopy

In the theoretical part of this study, the IR (400-4000 cm-1 region) and Raman (50-3500 cm-1 region) spectra of the ligands with the general formula C6H11NO2 (nipecotic acid) and C6H12N2O (nipecotamide) were recorded, and vibrational frequencies of the normal modes were determined. Assignments for the vibrational frequencies were proposed. The structural parameters (bond lengths and bond angles) and vibrational frequencies were obtained by using Gaussian03 computer program. The theoretical and experimental results were compared. Among the 6 isomeric and 1 tautomeric forms of nipecotic acid molecule, the NA-1 form was found to be the most stable one as a result of the DFT B3LYP/6-31G(d) level of calculations. The N-1 form was the most stable form among 4 isomers and 2 tautomers of nipecotamide molecule at the DFT B3LYP/6-311 + + G (d, p) level of calculations.In the experimental part of the study; the complexes of the general formula MX2L2 (M = Zn, X = Cl, Br, I, L = Nipecotic Acid / Nipecotamide) were obtained for the first time. IR spectra of the complexes were recorded, vibrational frequencies and normal modes were determined. C, H, N analysis results were given. Due to the complex formation, shiftings in the vibrational frequencies of the compounds with respect to the free ligand were observed. These shiftings vary depending on the halogen, and they were caused by the mechanical coupling of the metal-ligand bond vibrations with the ligand?s internal vibrations.In this study, the interaction energies in dimers of nipecotic acid and nipecotamide molecules were also investigated.