Molecular Packing of Phenoxazine: A Combined Single-Crystal / Crystal Structure Prediction Study

Phenoxazine is a heterocyclic molecule, which is used either as a parent molecule or with substituents for applications in various scientific fields: e.g., as a potential antioxidant. The purpose of this work is to present the molecular packing of phenoxazine within the crystalline state, as surprisingly no crystal structure is known so far. The crystal structure solution was performed by single-crystal X-ray investigations. Although the molecule has some potential for intermolecular hydrogen bonding, the observed structure is the classical herringbone packing typical for rodlike conjugated molecules. However, severe substitutional disorder of oxygen and nitrogen atoms is observed over their two opposite positions within the molecule. To get deeper insight into this disorder phenomenon, theoretical studies were performed, including crystal structure prediction using state of the art density functional theory techniques. The theoretical investigations confirm the experimentally observed 50% occupancy of the oxygen and nitrogen atoms.