β-Polymorph of phenazepam: A powder study

Abstract

The title compound [systematic name: 7-bromo-5-(2-chloro-phen-yl)-1H-1,4- benzodiazepin-2(3H)-one] (β-polymorph), C15H 10BrClN2O, has been obtained via cryomodification of the known α-polymorph of phenazepam [Karapetyan et al. (1979). Bioorg. Khim. 5, 1684-1690]. In both polymorphs, the molecules, which differ only in the dihedral angles between the aromatic rings [75.4 (2)° and 86.2 (3)° in the α- and β-polymorphs, respectively], are linked into centrosymmetric dimers via N - H⋯O hydrogen bonds. In the crystal structure of the β-polymorph, weak inter-molecular C - H⋯O hydrogen bonds further link these dimers into layers parallel to bc plane.