Evidence of low temperature phase transition in 2,6-dimethylpyrazine - picric acid cocrystal by means of temperature dependent investigations: X-ray, DSC and IR

• Published in: Journal of molecular structure Vol. 1228; p. 129432
• Main Authors: Pawlukojć, A., Hetmańczyk, J., Hetmańczyk, Ł., Nowicka-Scheibe, J., Maurin, Jan K., Schilf, W., Trzybiński, D., Woźniak, K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.03.2021
• Subjects: 2,6-Dimethylpyrazine-picric acid cocrystal; Phase transition; Raman spectroscopy; Temperature dependent IR spectroscopy, DFT calculation; X-ray diffraction; X-ray diffraction; Temperature dependent IR spectroscopy, DFT calculation; Raman spectroscopy; 2,6-Dimethylpyrazine-picric acid cocrystal; Phase transition
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2020.129432

•New 2,6-dimethylpyrazine - picric acid cocrystal was synthezed and investigated.•DFT calculation for solids state model was performed.•Low temperature phase transition was observed.•Full vibrational analysis was performed.•Activation energy for reorientation of CCH3bending vibration was obtained. In the present paper the structural and dynamical properties of crystalline 2,6–dimethylpyrazine - picric acid cocrystal are described. The title cocrystal crystallizes in centrosymmetric monoclinic P21/c space group. The X-ray diffraction and NMR spectroscopy show the presence of protonated form of 2,6-dimethypyrazine and deprotonated form of picric acid molecules. The Hirshfeld surface analysis for determine of intermolecular contacts was performed. Low temperature phase transition was observed and described by temperature dependent investigations: X-ray diffraction, different scanning calorimetry (DSC) and IR spectroscopy. The vibrational properties of cocrystal were investigated by use of IR and Raman spectroscopies, as well as density functional theory (DFT) with periodic boundary conditions. Activation energy for reorientational motion of CH3 group was determined from the band shape analysis of CCH3 bending vibration. [Display omitted]