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

Abstract 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∙∙∙O/O–H∙∙∙N strong hydrogen bonds and other intermolecular interactions such as H∙∙∙H, C–H∙∙∙π, π∙∙∙π and lone-pair∙∙∙π 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.