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, C(11)H(8)N(2)O(4), (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, C(13)H(12)N(2)O(4), (II), and dimethyl 1-(4-methyl­phen­yl)-1H-pyrazole-3,4-di­carboxyl­ate, C(14)H(14)N(2)O(4), (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, C(12)H(14)N(6)O(3), (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.