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). [ABSTRACT FROM AUTHOR]