β-Polymorph of phenazepam: a powder study

THE TITLE COMPOUND [SYSTEMATIC NAME: 7-bromo-5-(2-chloro-phen-yl)-1H-1,4-benzodiazepin-2(3H)-one] (β-polymorph), C(15)H(10)BrClN(2)O, 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 mol-ecules, 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.