4-[2,3-Dibromo-3-(4-bromophenyl)propanoyl]-2-phenyl-1,2,3-oxadiazol-2-ium-5-olate

In the title compound, C17H11Br3N2O3, the whole molecule is disordered over two positions with a refined occupancy ratio of 0.770 (5):0.230 (5). In the major component, the 1,2,3-oxadiazolidine ring is essentially planar [maximum deviation = 0.017 (6) Å] and makes dihedral angles of 22.5 (3) and 70.2 (3)° with the 4-bromophenyl and phenyl rings, respectively. In the minor component, the corresponding values are 18.9 (11) and 84.9 (12)°. In the crystal, intermolecular C—H⋯Br hydrogen bonds link the molecules into ribbons along [010]. There is a short O⋯N contact [2.83 (3) Å] in the minor component. In the major component, the molecular structure is stabilized by an intramolecular C—H⋯O hydrogen bond, which forms an S(6) ring motif.

In the title compound, C 17 H 11 Br 3 N 2 O 3 , the whole molecule is disordered over two positions with a refined occupancy ratio of 0.770 (5):0.230 (5). In the major component, the 1,2,3oxadiazolidine ring is essentially planar [maximum deviation = 0.017 (6) Å ] and makes dihedral angles of 22.5 (3) and 70.2 (3) with the 4-bromophenyl and phenyl rings, respectively. In the minor component, the corresponding values are 18.9 (11) and 84.9 (12) . In the crystal, intermolecular C-HÁ Á ÁBr hydrogen bonds link the molecules into ribbons along [010]. There is a short OÁ Á ÁN contact [2.83 (3) Å ] in the minor component. In the major component, the molecular structure is stabilized by an intramolecular C-HÁ Á ÁO hydrogen bond, which forms an S(6) ring motif.

Comment
Sydnones are mesoionic heterocyclic aromatic chemical compounds. The study of sydnones still remains a field of interests because of their electronic structures and also because of the varied types of biological activities displayed by some of them (Rai et al., 2008). Recently sydnone derivatives were found to exhibit promising antimicrobial properties (Jyothi et al., 2008). Since their discovery, sydnones have shown diverse biological activities and it is thought that the meso-ionic nature of the sydnone ring promotes significant interactions with biological systems. Because of wide variety of properties displayed by sydnones we were prompted to synthesize a new chalcone containing a sydnone type ring. Propenones are prepared by the condensation of 4-acetyl-3-arylsydnones with appropriately substituted aromatic aldehydes in an ethanol medium employing sodium hydroxide as catalyst. Bromination of these propenones were carried out using bromine in glacial acetic acid medium to give dibromochalcones (Rai et al., 2007).
The bond lengths (Allen et al., 1987) and angles are within normal ranges and are comparable to the closely related structure (Goh et al., 2010). The molecular structure is stabilized by an intramolecular C10A-H10A···O2A hydrogen bond, which forms an S(6) ring motif.
Experimental 1-(3-Phenylsydnon-4yl)-3-(p-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 h. The separated solid was filtered, washed with methanol and dried. It was then recrystallized from ethanol. Crystals suitable for X-ray analysis were obtained from 1:2 mixtures of DMF and ethanol by slow evaporation.

Refinement
All the H atoms were positioned geometrically [C-H = 0.93 to 0.98 Å] and were refined using a riding model, with U iso (H) = 1.2 U eq (C). The whole molecule is disordered over two positions with a refined ratio of 0.770 (5):0.230 (5). Rigidity, supplementary materials sup-2 similarity and simulation restraints were applied. The possibility of a supercell in which the whole-molecule disorder would be no longer exit was addressed by examining the h0l, 0kl, hk0 precession layers to ensure there are no rows of weak reflections between the rows that represent the current unit cell. No such supercell reflections were found. This finding is consistent with the fact that if such a supercell exists, the occupanies of the major and minor components would be the same.
However the refined occupanies are 0.770 (5): 0.230 (5) disproving the existence of a supercell. Fig. 1. The molecular structure of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. Both major and minor components are shown. Intramolecular interaction is shown in dashed line.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.