Solid solutions of quasi-isomorphous diastereomeric salts - kinetics versus thermodynamics

Attempts of racemic resolution by a fractional crystallization of diastereomeric salts of enantiopure resolving agent very often leads to precipitation of solid solutions with different ratios of both diastereomeric salts. Structural investigations of solid solutions can be helpful for a better understanding of the chiral discrimination mechanism which is useful for the rationalization of optical resolution. Based on the crystal structures of a few related solid solutions of brucinium diastereomeric salts and the corresponding diastereomeric salts factors influencing the kinetics and thermodynamics on the molecular recognition leading to the solid solution formation are proposed.