Structure of 2,4-dimethyl-1H-naphtho[2,3-b][1,4]diazepine hydropicrate. Solid-state assembly via C–H ⋯ O hydrogen bonding

Abstract

Crystal structure determination, semiempirical AM1 and PM3 calculations have been performed on 2,4-dimethyl-1H-naphtho[2,3-b][1,4]diazepine hydropicrate. The two molecules are almost planar apart from two NO₂ and CH₃ groups. The NO₂ plane makes an angle of 36.2° and 44.3° with the least squares plane of the ‘phenyl’ ring. The naphthodiazepine molecule and the picrate acid molecule are intermolecularly linked by one N–H ⋯ O and four C–H ⋯ O hydrogen bonds and form polar ribbons parallel to the [110] direction. The ribbons are linked by intermolecular C–H ⋯ O hydrogen bonds about a centre of inversion and the ensemble forms layers. These layers are weakly bound by van der Waals' interactions and undergo a reversible martensitic-type transition upon heating. During this transition the colour of the crystal changes from dark orange to yellow. AM1 and PM3 calculations on the dimers reproduce, with acceptable approximation, the main features of the structure.