Structural investigations of chloranilic acid pyrazine cocrystal and ferroelectric 2-methylbenzimidazole

The purpose of the project was to determine the crystal structures at variable temperatures and investigate the potential structural phase transitions in chloranilic acid pyrazine cocrystal and single-component ferroelectric 2-methylbenzimidazole. The crystal structure of chloranilic acid pyrazine at 120 K was triclinic, P-1, with a=4.7684(2) Å, b=5.8402(3) Å, c=10.6897(5) Å, α=82.038(4)°, β=81.568(4)°, γ=76.938(4)°. It undergoes a phase transition from monoclinic space group C2/m to triclinic space group P-1. We used ideas of rigid bodies and distortion-mode amplitudes to understand what drives the phase transition. The crystal structure of 2-methylbenzimidazole was explored by variable temperature powder and single crystal X-ray diffraction, as well as by variable temperature solid-state NMR and proton spectra calculations. The crystal structure did not change between 120 K and 400 K and was likely to be monoclinic space group Pn.