Crystal structure of 10-ethyl-7-(9-ethyl-9H-carbazol-3-yl)-10H-phenothiazine-3-carbaldehyde

In the title compound, a phenothiazine moiety is linked to a planar carbazole unit (r.m.s. deviation = 0.029 Å) by a C—C single bond. Their mean planes are inclined to one another by 27.28 (5)°, and the phenothiazine moiety possesses a typical butterfly structure with a fold angle of 27.36 (9)° between the two benzene rings.

The title compound, C 29 H 24 N 2 OS, contains a phenothiazine moiety linked to a planar carbazole unit (r.m.s. deviation = 0.029 Å ) by a C-C single bond. The phenothiazine moiety possesses a typical non-planar butterfly structure with a fold angle of 27.36 (9) between the two benzene rings. The dihedral angle between the mean planes of the carbazole and phenothiazine units is 27.28 (5) . In the crystal, molecules stack in pairs along the c-axis direction, linked by offset interactions [intercentroid distance = 3.797 (1) Å ]. There are C-HÁ Á Á interactions present linking these dimers to form a three-dimensional structure.

Chemical context
Phenothiazine, related to the thiazine class of heterocyclic compounds, is very important as it occurs in various antipsychotic drugs. Phenothiazine derivatives have been used in dye-sensitized solar cells to study the effect of conjugated linkers on device performance (Kim et al., 2011;Hagfeldt et al., 2010). One phenothiazine derivative (MCDP) is used to measure the activity of monoamine oxidase in blood (Fujii et al., 1993). They are also used as neuroleptics, sedatives, analgesics, anti-emetics and antihistamines (Harris & Klein, 1987). Triflupromazine phenothiazine hydrochloride is one of the most potent tranquilizer drug molecules (Phelps & Cordes, 1974). The phenothiazine derivative thiethylperazine has the properties of an anti-emetic and is widely used for the control of post-operative vomiting, in radiation therapy and vomiting associated with malignant disease (McDowell, 1970(McDowell, , 1978. N-Alkylamino carbazoles show significant anti-convulsant and diuretic activity (Shoeb et al., 1973). One of them, rimcazole, is a well known anti-pyretic and neuroleptic agent (Ferris et al., 1986). In view of this interest, we have synthesized the title phenothiazine derivative and report herein on its crystal structure.

Figure 1
The molecular structure of the title compound, with the atom labelling and displacement ellipsoids drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ).
phenothiazine unit, and 2293 hits for compounds containing a carbazole unit. Out of these entries, six compounds were found to possess both phenothiazine and carbazole ring systems, and one compound contains all three units, phenothiazine, carbazole and a carbaldehyde unit, but with the carbazole unit linked directly to the N atom of the phenothiazine unit, viz. 10-(9-hexyl-9H-carbazol-3yl)-10H-phenothiazine-3-carbaldehyde (IWABUF; Karuppasamy et al., 2017).

Synthesis and crystallization
To a mixture of 7-bromo-10-ethyl-10H-phenothiazine-3carbaldehyde (3 g, 0.0089 mol), 9-ethyl-9H-carbazole-3boronic acid pinnacol ester (3.17 g, 1.1 eq.), Pd(PPh 3 ) 4 (518 mg, 5% mol) and K 2 CO 3 (2.48 g, 2 eq.) under high vacuum was added a mixture of toluene:water (2:1). The resulting mixture was heated to reflux under an N 2 atmosphere for ca 24 h. On completion of the reaction (monitored by TLC), it was quenched by addition of saturated doubledistilled H 2 O and extracted with dichloromethane. The organic phases were collected and washed with brine and dried over anhydrous Na 2 SO 4 and then concentrated. The product was purified by column chromatography on silica gel using ethyl acetate:n-hexane (12:88, v/v) as eluent, to give the title compound as a pale-yellow crystalline solid (yield 80%). It was characterized by 1 H NMR, 13 C NMR, IR and ESI-MASS. Brown block-like crystals of the title compound were obtained by slow evaporation at room temperature of a solution in dichloromethane and acetonitrile (1:1 v/v).