Proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals TMP-D2ca and DMP-H2ca

Abstract

The proton dynamics in one-dimensional hydrogen-bonding system in molecular co-crystals of tetramethylpyrazine (TMP) with chloranilic acid (H 2 ca), as well as 2,6-dimethylpyrazine (DMP) with H 2 ca is studied by 35 Cl NQR and 2 H NMR spin-lattice relaxation measurements. No transfer motion of proton between the acid and base molecules is observed in DMP-H 2 ca, while the motion of the acid proton is excited in TMP-H 2 ca and the activation energy for the motion increases from 35 kJ mol −1 to 50 kJ mol −1 by the deuteration.

Experimental (X-ray, 13C CP/MAS NMR, IR, RS, INS, THz) and Solid-State DFT Study on (1:1) Co-Crystal of Bromanilic Acid and 2,6-Dimethylpyrazine

“…Due to the steric hindrance induced by the methyl groups, transition into such a synclinic state is highly undesirable, as it would require the reorientation of the whole 2,6-DMP units in the ∠ ab plane. Such an analysis claims a high stability of the studied phase and stays in line with Asaji’s 35 Cl NQR results . Such information is relevant from the point of view of crystal engineering, as it might suggest that the 2,6-DMP···BrA configuration tends to be very stable.…”

“…Such an analysis claims a high stability of the studied phase and stays in line with Asaji's 35 Cl NQR results. 42 Such information is relevant from the point of view of crystal engineering, as it might suggest that the 2,6-DMP•••BrA configuration tends to be very stable.…”

“…Such an assumption stays in line with the data reported for the isostructural, chloranilic acid analogue by Asaji and co-workers. 42 In the quoted paper, the spin−lattice 35 Cl NQR relaxation time measurements were performed across a wide temperature range, where it was concluded that the relaxation is dominated by lattice vibrations, suggesting no transfer motion of proton between the acid and base molecules.…”