Monday, 18 May 2015

Experimental (X-Ray, IR, RS, INS, THz) and Solid-State DFT Study on (1:1) Co-crystal of Bromanilic Acid and 2,6-Dimethylpyrazine

Katarzyna Łuczyńska , Kacper Drużbicki , Krzysztof Lyczko , and Jan Czeslaw Dobrowolski



Abstract


A combined structural, vibrational spectroscopy and solid-state DFT study of hydrogen-bonded complex of bromanilic acid with 2,6-dimethylpyrazine is reported. The crystallographic structure was determined by means of low-temperature single-crystal X-ray diffraction, which reveals the molecular units in their native protonation states, forming one-dimensional infinite nets of moderate-strength O∙∙∙H-N hydrogen bonds. The nature of the crystallographic forces, stabilizing the studied structure, has been drawn by employing the non-covalent interactions analysis. It was found that in addition to the hydrogen bonding, the intermolecular forces are dominated by stacking interactions and C-H∙∙∙O contacts. The thermal and calorimetric analysis was employed to probe stability of the crystal phase. The structural analysis was further supported by computationally assisted 13C CP/MAS NMR study, providing a complete assignment of the recorded resonances. The vibrational dynamics was explored by combining the optical (IR, Raman, TDs-THz) and inelastic neutron scattering (INS) spectroscopy techniques with the state-of-the-art solid-state density functional theory (DFT) computations. Despite of quasi-harmonic approximation assumed throughout the study, an excellent agreement between the theoretical and experimental data was achieved over the entire spectral range, allowing for deep and possibly thorough understanding of the vibrational characteristics of the system. Particularly, the significant influence of the long-range dipole coupling on the IR spectrum has been revealed. Based on a wealth of information gathered, the recent implementation of dispersion-corrected linear-response scheme has been extensively examined.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)