A second polymorph of (Z)-3-amino-4-(2-phenyl­hydrazinyl­idene)-1H-pyrazol-5(4H)-one

The mol­ecule of the title compound, C(9)H(9)N(5)O, is approximately planar (the r.m.s. deviation of all non-H atoms is 0.08 Å). The amine substituent is pyramidal at the N atom. An intra­molecular N—H(hydrazine)⋯O=C hydrogen bond is present. In the crystal, mol­ecules are connected via N—H⋯N and N—H⋯O hydrogen bonds, forming infinite layers parallel to (010). This polymorph is triclinic, space group P-1, whereas the previously reported form was monoclinic, space group P2(1)/c [Elgemeie et al. (2013 ▶). Acta Cryst. E69, o187], with stepped layers and a significantly lower density.