10H-Phenothiazine 5-oxide

In the title compound, C12H9NOS, the sulfoxide O atom is disordered over two sites with occupancies of 0.907 (4) and 0.093 (4). The dihedral angle betweeen the two aromatic rings is 18.40 (14)°. Different types of supramolecular interactions including intermolecular N—H⋯O hydrogen bonds and π–π contacts [centroid–centroid distances = 3.9096 (16) and 4.1423 (16) Å] between the aromatic rings of symmetry-related molecules are observed in the crystal structure.

In the title compound, C 12 H 9 NOS, the sulfoxide O atom is disordered over two sites with occupancies of 0.907 (4) and 0.093 (4). The dihedral angle betweeen the two aromatic rings is 18.40 (14) . Different types of supramolecular interactions including intermolecular N-HÁ Á ÁO hydrogen bonds andcontacts [centroid-centroid distances = 3.9096 (16) and 4.1423 (16) Å ] between the aromatic rings of symmetryrelated molecules are observed in the crystal structure.

Comment
The crystal structures of N-arylphenothiazine (Chu & Van der Helm, 1974, 1975, 1976, N-arylphenothiazine oxides (Chu et al., 1985;Wang et al., 2009) and dioxide (Zhu et al., 2007) have been reported, yet that of phenothiazine or its oxide has not been reported. The title compound (I) was obtained by the oxidation of phenothiazine in THF solution in air.
In the structure of I (Fig. 1), the sulfoxide O atom is disordered over two sites and the occupancy factors are 0.907 (4) (boat-axial S-O) and 0.093 (4) (boat-equatorial S-O). The same disorder in 10-acetyl-10H-phenothiazine 5-oxide was reported recently (Wang et al., 2009). The weighted average S-O distance of 1.471 Å in I is comparable to 1.466 Å in 10-acetyl-10H-phenothiazine 5-oxide, 1.498 (2) Å in 10-methylphenothiazine 5-oxide, and longer than 1.446 Å for dioxophenothiazinium cation (Zhu et al. 2007). The significantly shorter N-C distances in I than those in other N-arylphenothiazines or oxides are due to N-H instead of N-aryl groups (see the following table). For the same reason the dihedral angle betweeen the two benzene rings 18.40 (14) ° in I is smaller than those in the other compounds.

Experimental
A mixture of 1,3,5-benzenetricarboxylic acid (0.5 mmol) and phenothiazine (0.5 mmol) was dissolved in 10 ml THF. The solution changed from colorless to red in air in several hours. Brown crystals were obtained by slow evaporation for about 4 days at room temperature.

Refinement
The aromatic H atoms were generated geometrically (C-H 0.93, N-H 0.86 Å) and were allowed to ride on their parent atoms in the riding model approximations, with their temperature factors set to 1.2 times those of the parent atoms. The position of the oxygen atom is refined at two sites, with occupancy factors of 0.907 (4) and 0.093 (4). Fig. 1. Thermal ellipsoid plot of I. Displacement ellipsoids are drawn at the 50% probabability level.