Crystal and molecular structures of the monoclinic and orthorhombic modifications ofo-bromophenylazocarbamide

The crystal and molecular structures of two polymorphs ofo-bromophenylazocarbamide (C₇H₆N₃OBr) have been determined and refined by Fourier methods, using three-dimensional X-ray data collected at room temperature by photographic techniques. The unit cell parameters are, for the monoclinic modificationa = 25·20(1),b = 5·03(1),c = 14·01(1) Å, β = 105·5(1·0)°,Z = 8, space groupC2/c; for the orthorhombic modification,a= 14·02(1),b = 5·04(1),c = 24·32(3) Å,Z = 8, space groupPca2₁. In both polymorphs a rather large thermal effect is present, being greater for the orthorhombic phase. Corresponding bond distances and angles are equal in both structures to within 1σ. The double bond is virtually localized in theazo group, so that there is no conjugation between the bromophenyl and the carbamidic groups. NH···O hydrogen bonds link the molecules in ribbons, which are parallel in the monoclinic modification and mutually tilted (76·7 °) in the orthorhombic structure.