Four 1-aryl-1H-pyrazole-3,4-dicarboxylate derivatives: synthesis, molecular conformation and hydrogen bonding

Four 1-aryl-1H-pyrazole-3,4-dicarboxylate derivatives, one acid, two esters and a dicarbohydrazide have been synthesized starting from 3-aryl sydnones, and structurally characterized. There is an intramolecular O - H⋯O hydrogen bond in 1-phenyl-1H-pyrazole-3,4-dicarboxylic acid, C₁₁H₈N₂O₄, (I), and the molecules are linked into a three-dimensional framework structure by a combination of O - H⋯O, O - H⋯N, C - H⋯O and C - H⋯π(arene) hydrogen bonds. In each of the two esters dimethyl 1-phenyl-1H-pyrazole-3,4-dicarboxylate, C₁₃H₁₂N₂O₄, (II), and dimethyl 1-(4-methylphenyl)-1H-pyrazole-3,4-dicarboxylate, C₁₄H₁₄N₂O₄, (III), C - H⋯O hydrogen bonds lead to the formation of cyclic centrosymmetric dimers: in (III), one of the methoxycarbonyl groups is disordered over two sets of atomic sites having occupancies 0.71 (2) and 0.29 (2). An intramolecular N - H⋯O hydrogen bond is present in the structure of 1-(4-methoxyphenyl)-1H-pyrazole-3,4-dicarbohydrazide, C₁₂H₁₄N₆O₃, (IV), and the molecules are linked into a three-dimensional framework structure by a combination of N - H⋯O, N - H⋯N, N - H⋯π(arene) and C - H⋯O hydrogen bonds. Comparisons are made with the structures of a number of related compounds.