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Ni(II) complexes with 5,5′-bis(4-halogenphenyl)diazo-dipyrromethane have been synthesized and characterized by X-ray crystallography. All the complexes have similar crystal structures in which Ni(II) is square-planar by coordinating to two pyrrole and two azo nitrogen atoms. The azo-pyrroles of the ligands can be converted to the hydrazone tautomer after complexing nickel. Moreover, the C–H ··· Ni interaction played an important role in directing self-assembly of the complexes. The UV-Vis spectra of the complexes showed great difference with the metal complexes of pyrrol-2-imine.

Chlorine, bromine and iodine substituted derivatives of 5,5′-bisdiazo-dipyrromethane have been synthesized and their crystal structures were studied by X-ray crystallography. In the three structures, the 5,5′-bisdiazo-dipyrromethanes form interlocked dimers through quadruple N–H⋯N hydrogen bonds. The halogen⋯π synthons also provide a significant contribution to the resulting supramolecular motifs.

Quadruple N–H⋯N hydrogen bond driven self-assemblies of two 5,5′-bisdiazo-dipyrromethane compounds were studied by X-ray crystallography, 1H NMR and DFT calculation.