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

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-Cl-2; 3: X, Y = 2,4-Cl-2; 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 P2(1)/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 pi center dot center dot center dot pi stacking interactions are the most important intermolecular interactions in each of the six compounds. In the cases of 3 and 4, the pi center dot center dot center dot pi stacks are augmented by additional C-X center dot center dot center dot pi (X = Cl or Br) interactions, while in 4, the pi center dot center dot center dot pi stacks are linked by weak Br center dot center dot center dot Br interactions, and in 3, weak Cl center dot center dot center dot 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 pi systems point to significant strengths of the pi center dot center dot center dot pi 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 pi center dot center dot center dot pi interactions. The Hirshfeld analysis indicated further intermolecular contacts which fell outside the normal PLATON cutoff values.