2,3-Dibromo-3-(2-bromophenyl)-1-(3-phenylsydnon-4-yl)propan-1-one

In the title compound [systematic name: 2,3-dibromo-3-(2-bromophenyl)-1-(5-oxido-3-phenyl-1,2,3-oxadiazol-3-ium-4-yl)propan-1-one], C17H11Br3N2O3, the oxadiazole ring is essentially planar, with a maximum deviation of 0.003 (1) Å. The –CHBr–CHBr– chain and bromophenyl ring are disordered over two sets of sites with a refined occupany ratio of 0.756 (5):0.244 (5). The central oxadiazole ring makes dihedral angles of 54.07 (11) and 13.76 (18)° with the attached phenyl and the major component of the bromo-substituted benzene rings, respectively. The dihedral angle between the major and minor components of the bromophenyl rings is 13.4 (5)°. In the crystal structure, molecules are connected by C—H⋯O hydrogen bonds, forming [010] ribbons.


Comment
Sydnones constitute a well-defined class of mesoionic compounds that contain the 1,2,3-oxadiazole ring system. The study of sydnones still remains a field of interest because of their electronic structure and also because of the varied types of biological activities (Rai et al., 2008). Recently, sydnone derivatives were found to exhibit promising antimicrobial properties (Jyothi et al., 2008). Chalcones were obtained by the base-catalyzed condensation of 4-acetyl-3-aryl sydnones with aromatic aldehydes in alcoholic medium employing sodium hydroxide as catalyst at 0-50°C. Bromination of chalcones with bromine in glacial acetic acid afforded dibromo chalcones (Rai et al., 2007).
Experimental 1-(3 1 -Phenylsydnon-4 1 -yl)-3-(o-bromophenyl)-propen-1-one (0.01 mol) was dissolved in glacial acetic acid (25-30 ml) by gentle warming. A solution of bromine in glacial acetic acid (30% w/v) was added to it with constant stirring till the yellow colour of the bromine persisted. The reaction mixture was stirred at room temperature for 1-2 hours. The solid which separated was filtered, washed with methanol and dried. It was then recrystallized from ethanol. Colourless blocks of (I) were obtained from 1:2 mixtures of DMF and ethanol by slow evaporation.

Refinement
All H atoms were positioned geometrically [C-H = 0.93 or 0.98 Å] and were refined using a riding model, with U iso (H) = 1.2U eq (C). The dibromo substituted bromophenyl ring disordered over two sites with a refined occupany ratio of 0.756 (5):0.244 (5).

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (