1-Methyl-1H-indazole-3-carboxylic acid

The asymmetric unit of the title compound, C9H8N2O2, contains two molecules. In the crystal structure, both molecules form inversion dimers via pairs of O—H⋯O hydrogen bonds, and a C—H⋯O interation is also seen.

The asymmetric unit of the title compound, C 9 H 8 N 2 O 2 , contains two molecules. In the crystal structure, both molecules form inversion dimers via pairs of O-HÁ Á ÁO hydrogen bonds, and a C-HÁ Á ÁO interation is also seen.

S1. Comment
Methyl indazole carboxylic acid is an important pharmaceutical intermediate: many of its derivatives have biological activity and be used as a variety of drugs. We report here the crystal structure of the title compound, (I). There are O-H···O intermolecular H bonds in the structure between the hydrogencarboxylates forming the paired molecules that are situated on the crystallographic inversion centres ( Table 1). The molecular structure of (I) is shown in Fig. 1.

S2. Experimental
We prepared the title compound according to the literature method (Rousseau & Lindwall, 1950). Colourless blocks of (I) were obtained by slow evaporation of an petroleum/metanhol solution.

Figure 1
A view of the molecular structure of (I), showing displacement ellipsoids at the 30% probability level (arbitrary spheres for the H atoms).

Crystal data
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.