Metal-Involved Solvothermal Interconversions of Pyrazinyl Substituted Azole Derivatives: Controllability and Mechanism

Under different solvothermal reaction conditions I (60 °C for 48 h) and II (140 °C for 72 h), the dipyrazinyl compounds bearing oxadiazole and triazole spacers, that is, 2,5-bis(2-pyrazinyl)-1,3,4-oxadiazole (L1) and 4-amino-3,5-bis(2-pyrazinyl)-1,2,4-triazole (L2), may suffer reversible conversions in the presence of certain metal salts. Other related derivatives such as 3,5-bis(2-pyrazinyl)-1,2,4-triazole-4-yl-N-pyrazinamide (HL4) and pyrazine-2-carboxylic acid (HL0) can also be (in situ) obtained from L1 and L2, respectively, under conditions I and II. Beyond this, N,N′-bis(2-pyrazineamide) (H2L3) can be in situ afforded from both precursors L1 and L2, and thus, may be considered as the potential intermediate during the interconversions. The possible mechanisms and influence factors of these reactions have also been established based on the experimental results. As a result, a variety of crystalline materials (co-crystals and coordination complexes) with attractive supramolecular architectures have been isolated by regulating the reaction conditions well (reaction temperature, metal ion, and even inorganic counteranion).