Complex network of hydrogen bonds in 3-aminopyrazole-4-carboxylic acid.

3-Aminopyrazole-4-carboxylic acid, C4H5N3O2, crystallized in the non-centrosymmetric space group P21 in the zwitterionic form. Intermolecular N--H...O hydrogen bonds with N...O distances of 2.768 (2) and 2.747 (2) A link molecules into two sets of chains propagating along [110] and [110]. The two sets of chains are crosslinked by strong hydrogen bonds. A complex network of hydrogen bonds ensues. There is a single intramolecular hydrogen bond. The pyrazole core is closely planar; the dihedral angle between the best-fit core planes of the molecules making up the two chains is 82.2 (1) degrees. The dihedral angles between the core plane and the planes of the carboxylate group and the amino group are in the region of 2 and 37 degrees, respectively.