000858950 001__ 858950 000858950 005__ 20240404204704.0 000858950 0247_ $$2doi$$a10.1039/C8CE00040A 000858950 0247_ $$2WOS$$aWOS:000435950800013 000858950 0247_ $$2altmetric$$aaltmetric:33967814 000858950 037__ $$aFZJ-2018-07776 000858950 082__ $$a540 000858950 1001_ $$00000-0001-6206-8391$$aRok, M.$$b0$$eCorresponding author 000858950 245__ $$aCrystal structural analysis of methyl-substituted pyrazines with anilic acids: a combined diffraction, inelastic neutron scattering, 1 H-NMR study and theoretical approach 000858950 260__ $$aLondon$$bRSC$$c2018 000858950 3367_ $$2DRIVER$$aarticle 000858950 3367_ $$2DataCite$$aOutput Types/Journal article 000858950 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article$$bjournal$$mjournal$$s1712214230_21204 000858950 3367_ $$2BibTeX$$aARTICLE 000858950 3367_ $$2ORCID$$aJOURNAL_ARTICLE 000858950 3367_ $$00$$2EndNote$$aJournal Article 000858950 520__ $$aThe crystal and molecular structures of (1) 2-methylpyrazine (2MP) with 2,5-dichloro-3,6-dihydroxy-p-quinone (chloranilic acid, CLA), (2) 2-methylpyrazine (2MP) with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA), (3) 2,3,5-trimethylpyrazine (TrMP) with 2,5-dichloro-3,6-dihydroxy-p-quinone (chloranilic acid, CLA), and (4) 2,3,5-trimethylpyrazine (TrMP) with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA) were analyzed in terms of the number of independent methyl groups in their crystal structure. The inelastic neutron back-scattering spectra at low temperature (4–40 K) were discussed in terms of methyl group tunnelling. The INS spectra were compared with the temperature dependence of the 1H-NMR spin–lattice relaxation time, particularly at low temperatures, where CH3 tunnelling is postulated. The infrared and Raman spectra at room temperature were recorded for all complexes under investigation. Furthermore, the vibrational spectra were discussed in terms of the structure of molecules and their interactions. The structural phase transition of the TrMP·CLA complex at 171/175 K (cooling/heating) was characterized by DSC and single-crystal X-ray diffraction. Full-geometry optimization was carried out in the solid state in order to obtain the minimum structures and bonding properties. The results are in very good agreement with the experimental data. The infrared spectrum in the harmonic approximation was calculated and a comparative vibrational analysis was performed. 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