Stability and phase transition investigation of olanzapine polymorphs

Abstract

We use electrical embedded-fragment QM method with both DFT/ωB97XD/6-31G* and MP2/6-31G* to investigate the phase transformations of olanzapine. Gibbs free energy calculations predict that form I is always the most stable structure and form II is the least stable one, while form IV is more stable than form III below about 200 K but less stable above this temperature, implying a polymorphic phase transformation. This may account for why form IV has only recently been discovered as crystallizing from a polymer-based molecular dispersion. The proposed methods may provide guidance for experiments and thus promote the study of phase transitions of pharmaceutical molecules.