Energetics of Glycine Co-crystal or Salt Formation with Two Regioisomers: Fumaric acid and Maleic acid

Multicomponent crystals have received significant attention in recent years, given their considerable potential to develop new products or improve the properties of known ones. Many studies have examined the synthesis and structure of multicomponent (mostly binary) crystals. The thermodynamic aspects related to the driving force for their formation and stability are, however, still relatively unexplored. This work describes a structure–energetics study of binary crystals consisting of glycine (Gly) and fumaric acid (FA) or maleic acid (MA), two regioisomers with different proton transfer abilities. Single-crystal X-ray diffraction experiments showed that the mechanochemically synthesized materials corresponded to a new FA:Gly2 cocrystal and a MA:Gly salt that had been previously prepared by crystallization from solution. A packing analysis further suggested that the stoichiometry difference (1:2 vs 1:1) is possibly related to differences in hydrogen bonding ability between FA and MA. Calorimetric and solu...