Two polymorphic forms of 2,5-bis(4-methoxycarbonylphenyl)-1,3,4-oxadiazole.

The title compound [systematic name: dimethyl 4,4'-(1,3,4-oxadiazole-2,5-diyl)diphenylenedicarboxylate], C(18)H(14)N(2)O(5), crystallizes under similar conditions in two different orthorhombic crystalline forms. In both forms, the molecule consists of two equivalent parts. In form 1, these parts are related by a twofold axis of space group Pbcn, and in form 2, by a mirror plane of space group Cmc2(1). The O atom of the oxadiazole ring occupies a special position on the twofold axis and on the mirror plane in forms 1 and 2, respectively.