Nitro–ring inter–laminar π,π–interactions affecting the crystal building of N–(p–nitro–benzyl)–iminodiacetato–nickel(II) complex. Synthesis, characterization, Hirshfeld surface analysis, time–dependent–DFT and optical bandgap energy plots of H2NBIDA and their Ni(II) binary and ternary complexes.

The nickel(II) binary [Ni(NBIDA)(H ₂ O) ₃ ]·0.5H ₂ O ( 1 ), and ternary [Ni(NBIDA)(Him) ₃ ] ( 2 ) complexes, where NBIDA =  N –( p –nitro–benzyl)–iminodiacetato(2–) and Him = imidazole, have been isolated from the stoichiometric reactions between Ni(II) hydroxy–carbonate and H ₂ NBIDA chelating ligand in aqueous media without and with imidazole respectively. The crystalline samples of both compounds have been characterized by means of elemental analysis, FTIR, UV–visible, TGA and single crystal (complex 1 ) x–ray crystallography. The physico–chemical results reveal the distorted octahedral environment around the Ni(II) ion for both complexes which further confirmed through the optimization of molecular structure through the Density Functional Theory (DFT). The crystal packing and space group of complex 1 (Monoclinic, space group P 2 ₁ /c ) differs from those of previously reported similar nickel(II) chelates [Ni(L)(H ₂ O) ₃ ] ]·H ₂ O, (L = FBIDA, CBIDA) (Orthorhombic Pca 2 ₁ ) can be attributed to the effect of nitro–ring inter–laminar π,π–interactions involved in complex ( 1 ). The fac –NO ₂ conformation of IDA moiety observed through their molecular crystal structure. Besides to this, the distinct intermolecular forces–specifically, hydrogen bonding interactions, 2D fingerprint plots, and supramolecular architecture have been examined using Hirshfeld surface analysis. In order to corroborate the experimental findings with theoretical studies, the molecular simulation processes employing DFT/B3LYP/3–21G ^+* were performed to obtain the distinct geometry optimizations and other relevant parameters, such as highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO–LUMO) energy gaps, time dependent density functional theory (TD–DFT), single point energy (SPE) etc. The direct and indirect optical bandgap energy plots for both Ni(II) complexes ( 1 ) and ( 2 ) as well as for H ₂ NBIDA were measured and discussed.