2-(1H-Tetrazol-1-yl)acetic acid monohydrate

The crystal structure of the title compound, C3H4N4O2·H2O, exhibits O—H⋯O and O—H⋯N hydrogen bonds, which lead to the formation of a two-dimensional network parallel to the bc plane. The dihedral angle between the ring and the carboxylic acid group is 84.6 (14)°.

In the title compound the carboxyl functional group is almost perpendicular to the tetrazole heterocycle with a dihedral angle of 87.3 (2)°. The O3-H3B···N2 hydrogen bond anchors the water molecule to the tetrazole heterocycle. Two intermolecular hydrogen bonds (O1-H1A···O3 and O3-H3A···O2) connect the water molecule and two carboxyl groups from the neighboring asymmetric unit, forming layers with louver-like network (Fig. 2).

Experimental
A procedure similar to the previously published method of Jústiz et al. (1997) was applied. To a solution of 2-aminoacetic acid (7.5 g, 0.1 mol) in 50 ml acetic acid was added triethoxymethane (32.4 g, 0.22 mol) and sodium azide (7.15 g, 0.11 mol). The mixture was refluxed for 3.0 h at 80°C. Active carbon was used to discolor the mixture, which was then refluxed for another 10 minutes. Heating was stopped and cooled to room temperature, the mixture was filtered to remove the active carbon and concentrated hydrochloric acid was trickled into the filtrate and a white solid product precipitated out. The precipitate was extracted by ethyl acetate and washed with saturated solution of sodium bicarbonate, brine, and then dried over MgSO 4 . Evaporation of the solvent in vacuum afforded the 2-(1H-tetrazol-1-yl) acetic acid compound. The pale yellow single crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of a solution in the 3:7 (v/v) mixture of petroleum ether and ethyl acetate.

Refinement
In the absence of significant anomalous dispersion effects, Friedel pairs were averaged. Hydrogen atom positions were calculated geometrically and were set to ride on the associated C atoms, with U iso (H)= 1.2 U iso (C). The H atoms on O were located in difference electron density maps and were refined freely with isotropic displacement parameters.

Figure 2
Packing diagram for the title compound. Hydrogen bonds are denoted by dashed lines.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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.  (3)