Co-crystallization of a neutral mol­ecule and its zwitterionic tautomer: structure and Hirshfeld surface analysis of 5-methyl-4-(5-methyl-1H-pyrazol-3-yl)-2-phenyl-2,3-di­hydro-1H-pyrazol-3-one 5-methyl-4-(5-methyl-1H-pyrazol-2-ium-3-yl)-3-oxo-2-phenyl-2,3-di­hydro-1H-pyrazol-1-ide monohydrate

The title compound, 2C(14)H(14)N(4)O·H(2)O, comprises a neutral mol­ecule containing a central pyrazol-3-one ring flanked by an N-bound phenyl group and a C-bound 5-methyl-1H-pyrazol-3-yl group (at positions adjacent to the carbonyl substituent), its zwitterionic tautomer, whereby the N-bound proton of the central ring is now resident on the pendant ring, and a water mol­ecule of crystallization. Besides systematic variations in geometric parameters, the two independent organic mol­ecules have broadly similar conformations, as seen in the dihedral angle between the five-membered rings [9.72 (9)° for the neutral mol­ecule and 3.32 (9)° for the zwitterionic tautomer] and in the dihedral angles between the central and pendant five-membered rings [28.19 (8) and 20.96 (8)° (neutral mol­ecule); 11.33 (9) and 11.81 (9)°]. In the crystal, pyrazolyl-N—H⋯O(carbon­yl) and pyrazolium-N—H⋯N(pyrazol­yl) hydrogen bonds between the independent organic mol­ecules give rise to non-symmetric nine-membered {⋯HNNH⋯NC(3)O} and {⋯HNN⋯HNC(3)O} synthons, which differ in the positions of the N-bound H atoms. These aggregates are connected into a supra­molecular layer in the bc plane by water-O—H⋯N(pyrazolide), water-O—H⋯O(carbon­yl) and pyrazolyl-N—H⋯O(water) hydrogen bonding. The layers are linked into a three-dimensional architecture by methyl-C—H⋯π(phen­yl) inter­actions. The different inter­actions, in particular the weaker contacts, formed by the organic mol­ecules are clearly evident in the calculated Hirshfeld surfaces, and the calculated electrostatic potentials differentiate the tautomers.