Three new co-crystals of 2,3,5,6-tetramethyl pyrazin with different substituted aromatic compounds_ crystal structure, spectroscopy and Hirshfeld analysis

Co-crystallizations of 2,3,5,6-tetramethyl pyrazin (TMP) with different substituted aromatic compounds [3,5-dinitrosalicylic acid (DNS), 5-chlorosalicylic acid (CSA) and 3,5-dichlorosalicylic acid (DCA)] have been performed, resulting in the formation of three co-crystals (TMP : DNS = 1:1 for 1; TMP : CSA = 1:2 for 2; TMP : DCA = 1:2 for 3). Those newly co-crystals were characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analyses (TGA), UV-Vis spectroscopy and X-ray diffraction (XRD). The Hirshfeld surface analysis revealed that N-H center dot center dot center dot O/O-H center dot center dot center dot N strong hydrogen bonds and other intermolecular interactions such as H center dot center dot center dot H, C-H center dot center dot center dot pi, pi center dot center dot center dot pi and lone-pair center dot center dot center dot pi participated in a cooperative way to stabilize the supramolecular structures. Additionally, thermodynamic results indicated that the halogen bonding exerted a positive effect on the stability of co-crystal structures, further improving the release process of pyrazine spices. This work provided a co-crystal strategy for the solidification of liquid pyrazine-related spices for broader applications. (C) 2021 Published by Elsevier B.V.