A co-crystal strategy for the solidification of liquid pyrazine derivatives: X-ray structures and Hirshfeld surface analyses

Abstract

Here we described a co-crystal strategy for the solidification of liquid 2,3-dimethylpyrazine (2,3-DMP), 2,5-dimethylpyrazine (2,5-DMP), 2,6-dimethylpyrazine (2,6-DMP) with the poly-substituted salicylic acids [3,5,6-trichlorosalicylic acid (TCSA) and 3,5-dinitrosalicylic acid (DNSA)] under identical conditions. Those newly grown co-crystals (2,3-DMP:TCSA = 1:1 for 1; 2,5-DMP:TCSA = 1:2 for 2; 2,6-DMP:DNSA = 1:1 for 3) were characterized by single-crystal X-ray diffraction. The structure determination shows that strong O-H⋯N hydrogen bonds play an important role in connection of pyrazine derivatives and poly-substituted salicylic acids. Moreover, aromatic cycle stacking interactions play a crucial role in the 3D supramolecular network. Hirshfeld surfaces and fingerprint plots of the reported co-crystals were analyzed, which showed that O-H⋯N, C-H⋯O, H⋯H, H⋯Cl and aromatic cycle stacking intermolecular interactions are the main stabilizing factors of the co-crystal structures. The melting points studies showed that the co-crystal strategy is effective for solidification of liquid pyrazine derivatives.