Vibrational spectroscopic and DFT calculation studies of cobalt(II) complexes with 3-hydroxypicolinic acid

Two cobalt(II) complexes with 3-hydroxypicolinic acid (3-hydroxypyridine-2-carboxylic acid, 3-OHpicH), trans-[Co(3-OHpic)2(py)2] (2) and cis-[Co(3-OHpic)2(4-pic)2] (3) (py = pyridine; 4-pic = 4-picoline or 4-methylpyridine), previously synthesized and characterized by X-ray diffraction, are here studied by Raman and mid-infrared spectroscopy with the help from the corresponding DFT vibrational calculations using B3LYP/6-311G(d,p) computational model. Intramolecular O–H⋯O hydrogen bond appears in both complexes 2 and 3, while weak C–H⋯O hydrogen bonds assemble molecules of 2 or 3 into 3D architecture. A complete presentation of all Raman, infrared and theoretical results is given for complex 3. The measured spectra are shown, relative intensities and bandwidths are discussed and the assignment of vibrational bands is given on the basis of the DFT calculations. The calculated spectra agree very well with the presented experimental findings, thanks to the suitable grouping of modes. The same vibrational calculations also reveal insignificant influence of H → CH3 substitution for the spectroscopic characterization of the complex. A careful study of differences between calculated and observed wavenumbers suggests that modified single-factor scaling is actually better than the classic multi-factor scaling approach.

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► trans-[Co(3-OHpic)2(py)2] (2) and cis-[Co(3-OHpic)2(4-pic)2] (3) were studied.
► Raman and mid-infrared spectra were recorded.
► DFT vibrational calculations performed, using B3LYP/6-311G(d,p) computational model.
► The assignment of vibrational bands is given on the basis of the DFT calculations.
► Insignificant influence of H → CH3 substitution for the spectroscopic characterization of 3.