Quaternary phase diagrams as a tool for ionic cocrystallization: the case of a solid solution between a racemic and enantiopure ionic cocrystal

In this study, a general isothermal quaternary phase diagram of etiracetam (racemate)-levetiracetam (S-enantiomer)-CaCl2∙2H2O-water is generated to understand the crystallization thermodynamics of ionic cocrystal systems. Solubility surfaces are depicted clearly by the appliance of contour lines and various polyhedrons of the domains in the IQPD are delineated according to the eutectic points. The system shows a full solid solution between the racemic and enantiopure ionic cocrystals.