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 center dot H2O, 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)degrees for the neutral molecule and 3.32 (9)degrees for the zwitterionic tautomer] and in the dihedral angles between the central and pendant five-membered rings [28.19 (8) and 20.96 (8)degrees (neutral molecule); 11.33 (9) and 11.81 (9)degrees]. In the crystal, pyrazolyl-N-H center dot center dot center dot O(carbonyl) and pyrazolium-N-H center dot center dot center dot N(pyrazolyl) hydrogen bonds between the independent organic molecules give rise to non-symmetric ninemembered {center dot center dot center dot HNNH center dot center dot center dot NC3O} and {center dot center dot center dot HNN center dot center dot center dot HNC3O} 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 center dot center dot center dot N(pyrazolide), water-O-H center dot center dot center dot O(carbonyl) and pyrazolyl-N-H center dot center dot center dot O(water) hydrogen bonding. The layers are linked into a three-dimensional architecture by methyl-C-H center dot center dot center dot(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.