Synthesis, crystal structure and Hirshfeld surface analysis of the ortho-rhom-bic polymorph of 4-bromo- N -(4-bromo-benzyl-idene)aniline.

The crystal structure of the title compound, C 13 H 9 Br 2 N [systematic name: ( E )- N ,1-bis-(4-bromo-phen-yl)methanimine], is a second polymorph (Form II) crystallizing in the ortho-rhom-bic space group Pccn . The first polymorph (Form I) crystallizes in the monoclinic space group P 2 1 / c [Bernstein & Izak (1975 ▸). J. Cryst. Mol. Struct. 5 , 257-266; Marin et al. (2013 ▸). J. Mol. Struct. 1049 , 377-385]. The mol-ecule is disordered about an inversion center situated in the middle of the C=N bond, similar to the situation in the monoclinic polymorph: the C=N bond length is 1.243 (7) Å. In the crystal, mol-ecules stack along the b- axis direction and are linked by C-H⋯π inter-actions. The inter-atomic contacts in the crystal for both polymorphs were studied by Hirshfeld surface analysis and have notable differences. The solid-state fluorescence spectrum of Form II shows an emission peak at ca 469 nm. The two-photon absorption coefficient measured from the open aperture Z -scan technique is 1.3 × 10 -11 m W -1 , hence, Form II shows optical limiting behaviour.