Crystal structures and Hirshfeld surface analyses of halogen substituted azine derivatives, 1,4-bis(halophenyl)-2,3-diazabuta-1,3-dienes

Abstract

Abstract The crystal structures and Hirshfeld surface analyses are reported, from data collected at 100 K, of six 1,4-bis(X,Y-phenyl)-2,3-diazabuta-1,3-dienes (1–6), namely (1: X, Y=H, 4-Cl; 2: X, Y=3,4-Cl2; 3: X, Y=2,4-Cl2; 4: X, Y=H, 2-Br, H; 5: X, Y=H, 3-Br; 6: X, Y=H, 4-Br. The six halogen derivatives crystallise in the monoclinic group P21/c. In each case, the asymmetric unit is one half of the molecule, with the molecules lying across inversion centres, midway between the N–N bonds, with the central C–C=N–N=C–C fragments having all transoid conformations. Each of the six molecules deviates a little from overall planarity. The π···π stacking interactions are the most important intermolecular interactions in each of the six compounds. In the cases of 3 and 4, the π···π stacks are augmented by additional C–X···π (X=Cl or Br) interactions, while in 4, the π···π stacks are linked by weak Br···Br interactions, and in 3, weak Cl···Cl contacts are considered to be also involved in cementing the supra molecular arrangements. The short separations of the layers within the stacks and the extent of the overlaps of the π systems point to significant strengths of the π···π interactions. Comparisons with published structures of related chloro and fluoro compounds indicated similar results: related iodo derivatives, IC6H4CH=N–N=CHC6H4I do not possess as strong π···π interactions. The Hirshfeld analysis indicated further intermolecular contacts which fell outside the normal PLATON cutoff values.