Four 1-aryl-1-pyrazole-3,4-di-carboxyl-ate derivatives: synthesis, mol-ecular conformation and hydrogen bonding.

Four 1-aryl-1-pyrazole-3,4-di-carboxyl-ate derivatives, one acid, two esters and a dicarbohydrazide have been synthesized starting from 3-aryl sydnones, and structurally characterized. There is an intra-molecular O-H⋯O hydrogen bond in 1-phenyl-1-pyrazole-3,4-di-carb-oxy-lic acid, CHNO, (I), and the mol-ecules 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-1-pyrazole-3,4-di-carboxyl-ate, CHNO, (II), and dimethyl 1-(4-methyl-phen-yl)-1-pyrazole-3,4-di-carboxyl-ate, CHNO, (III), C-H⋯O hydrogen bonds lead to the formation of cyclic centrosymmetric dimers: in (III), one of the meth-oxy-carbonyl groups is disordered over two sets of atomic sites having occupancies 0.71 (2) and 0.29 (2). An intra-molecular N-H⋯O hydrogen bond is present in the structure of 1-(4-meth-oxy-phen-yl)-1-pyrazole-3,4-dicarbohydrazide, CHNO, (IV), and the mol-ecules 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.