2,3,5-Triphenyl-2H-tetrazol-3-ium bromide ethanol monosolvate

In the title compound, C19H15N4 +·Br−·C2H5OH, the tetrazole ring makes dihedral angles of 57.44 (9), 50.92 (9) and 4.65 (8)° with the attached phenyl rings. In the crystal, the cation and the anion are linked to each other by intermolecular C—H⋯Br hydrogen bonds into an infinite chain along the b axis. The anion and the ethanol solvent molecule are linked by an O—H⋯Br hydrogen bond. The crystal studied was an inversion twin with a refined component ratio of 0.632 (5):0.368 (5).

In the title compound, C 19 H 15 N 4 + ÁBr À ÁC 2 H 5 OH, the tetrazole ring makes dihedral angles of 57.44 (9), 50.92 (9) and 4.65 (8) with the attached phenyl rings. In the crystal, the cation and the anion are linked to each other by intermolecular C-HÁ Á ÁBr hydrogen bonds into an infinite chain along the b axis. The anion and the ethanol solvent molecule are linked by an O-HÁ Á ÁBr hydrogen bond. The crystal studied was an inversion twin with a refined component ratio of 0.632 (5):0.368 (5).

Related literature
For the biological activity of the triphenyltetrazolium ion, see: Mostafa (2007); Hassanien et al. (2003); Abbas et al. (2001). For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986

Abdel-Aziz
Comment 2,3,5-Triphenyltetrazolium ion is used as indicator of bacterial dehydrogenase activity and as a reagent in colorimetric determination method for glucose dehydrogenase. Moreover, triphenyltetrazolium ion is used as ion-pair reagent for determination of antimony in waste water (Mostafa, 2007;Hassanien et al., 2003;Abbas et al., 2001).
In the crystal (Fig. 2), the cation and the anion are linked to each other by intermolecular C9-H9A···Br1 and C11-H11A···Br1 hydrogen bonds into an infinite chain, running along the b axis, with atom Br1 as the bifurcated acceptor. The crystal packing is further stabilized by the intermolecular O1-H1O1···Br1 hydrogen bond, involving the ethanol O atom.

Experimental
Upon the addition of triphenyltetrazolium chloride solution (50 ml, 1×10 -2 M) to a solution of potassium bromide (50 ml), a whitish precipitate was formed. The precipitate was filtered off, washed with cold deionized water until no chloride ion was detected in the washing solution. The precipitate was dried under vacuum to give the title ion-pairs complex.
Colourless blocks suitable for an X-ray structural analysis were obtained by slow evaporation from ethanol.

Refinement
The O-bound H atom was located in a difference Fourier map and refined freely [O1-H1O1 = 0.77 (2) Å]. The remaining H atoms were positioned geometrically (C-H = 0.93, 0.96 and 0.97 Å) and refined using a riding model with U iso (H) = 1.2 or 1.5U eq (C). A rotating group model was applied to the methyl group. Seven outliers, (085), (022), (084), (043), (011), (042) and (094), were omitted in the final refinement. The crystal studied was an inversion twin with BASF of 0.368 (5).  The molecular structure of the title compound with atom labels and 50% probability displacement ellipsoids.

Figure 2
The crystal packing of the title compound. The dashed lines represent the hydrogen bonds. For clarity sake, hydrogen atoms not involved in hydrogen bonding have been omitted.  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 > σ(F 2 ) is used only for calculating R-factors(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.