Z/E‐Isomerism of 3‐[4‐(dimethylamino)phenyl]‐2‐(2,4,6‐tribromophenyl)acrylonitrile: crystal structures and secondary intermolecular interactions

The Z and E isomers of 3‐4‐(dimethylamino)phenyl]‐2‐(2,4,6‐tribromophenyl)acrylonitrile, C₁₇H₁₃Br₃N₂, ( 1 ), were obtained simultaneously by a Knoevenagel condensation between 4‐(dimethylamino)benzaldehyde and 2‐(2,4,6‐tribromophenyl)acetonitrile, and were investigated by X‐ray diffraction and density functional theory (DFT) quantum‐chemical calculations. The (Z)‐( 1 ) isomer is monoclinic (space group P2₁/n, Z′ = 1), whereas the (E)‐( 1 ) isomer is triclinic (space group P, Z′ = 2). The two crystallographically‐independent molecules of (E)‐( 1 ) adopt similar geometries. The corresponding bond lengths and angles in the two isomers of ( 1 ) are very similar. The difference in the calculated total energies of isolated molecules of (Z)‐( 1 ) and (E)‐( 1 ) with DFT‐optimized geometries is ～4.47 kJ mol^?1, with the minimum value corresponding to the Z isomer. The crystal structure of (Z)‐( 1 ) reveals strong intermolecular nonvalent Br…N 3.100 (2) and 3.216 (3) Å] interactions which link the molecules into layers parallel to (10). In contrast, molecules of (E)‐( 1 ) in the crystal are bound to each other by strong nonvalent Br…Br 3.5556 (10) Å] and weak Br…N 3.433 (4) Å] interactions, forming chains propagating along 110]. The crystal packing of (Z)‐( 1 ) is denser than that of (E)‐( 1 ), implying that the crystal structure realized for (Z)‐( 1 ) is more stable than that for (E)‐( 1 ).