1-[4-({4-[(E)-(2-Hydroxynaphthalen-1yl) methylideneamino] phenyl} sulfanyl)phenyl] ethanone

The title Schiff base compound, C25H19NO2S, crystallizes in a statistically disordered structure comprising keto and enol tautomeric forms. In the enol form, the benzenoid arrangment is promoted by a strong intramolecular O-H center dot center dot center dot N hydrogen bond and adopts an E conformation about the imine bond. In the keto form there is an intramolecular N-H center dot center dot center dot O hydrogen bond. In the crystal, an extended network of C-H center dot center dot center dot O hydrogen bonds stabilizes columns parallel to the c axis, forming large voids (there are four cavities of 108 angstrom 3 per unit cell) with highly disordered residual electron density. The SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65, 148-155] was used to eliminate the contribution of this electron density from the intensity data, and the solvent-free model was employed for the final refinement. The contribution of this undetermined solvent was ignored in the calculation of the unit-cell characteristics.