Wydział Chemii

Magdalena Rok

Grażyna Bator

Wanda Sawka-Dobrowolska

Piotr Durlak

Marcin Moskwa

Wojciech Medycki

Lucjan Sobczyk

Michaela Zamponi

2018

CrystEngComm

20

2016-2028

10.1039/c8ce00040a

Naukowa

Angielski

Artykuł

The 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 the methyl groups tunnelling. The INS spectra were compared with the temperature dependence of the 1H NMR spin-lattice relaxation time, especially at low temperature, where the CH3 tunnelling is postulated. The infrared and Raman spectra at room temperature were recorded for all complexes under study. Furthermore, the vibrational spectra have been discussed in terms of the structure of molecules and their interactions. The structural phase transition found for TrMP·CLA complex at 171/175 K (cooling/heating) has been characterized by the DSC, dilatometric and by the single-crystal X-ray diffraction methods. Full geometry optimization has been carried out in the solid state in order to obtain minimum structures and bonding properties. The results show a very good agreement with the experimental data. The infrared spectrum in harmonic approximation was calculated and a comparative vibrational analysis was performed. CRYSTAL09 vibrational results appear to be in good agreement with the experimental ones.

http://dx.doi.org/10.1039/c8ce00040a

https://www.rsc.org/