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.