Aqueous media synthesis of Ni(II) complexes of N–(p–methyl–phenethyl)–iminodiacetate(2-) chelate with or without N–heterocyclic donor ligands: Supramolecular architectures, molecular docking, Hirshfeld surfaces analysis, DFT overview and optical bandgap measurements.

The stoichiometric reactions between nickel(II) hydroxy–carbonate and N–(p–methyl–phenethyl)–iminodiacetic acid (H₂MEpheida) in aqueous media give greenish color crystal of binary complex [Ni(MEpheida)(H₂O)₃] (1) which turns on ternary complex [Ni(MEpheida)(Him)₂(H₂O)]·2H₂O (2) on addition of imidazole (Him) ligand in the ratio of 1:1:3 for H₂MEpheida, Ni(II) salt and Him respectively. The synthesized metal complexes have been characterized by various analytical, spectroscopic viz., ¹HNMR, FTIR, UV–vis., thermogravimetry and single–crystal X–ray diffraction techniques. The crystal pattern of complex (1) differs from the related ternary complex (2) can be attributed to the ligation of N–heterocyclic ligands. The distorted octahedral geometry around the Ni(II) ion scrutinized through the single crystal X–ray analysis. As speculated, the IDA (Iminodiacetate(2-)) arm of chelate adopted fac–NO₂ conformation in both complexes (1) and (2). Furthermore, energy frameworks and Hirshfeld surface analysis has been utilized to scrutinized the unique intermolecular forces, specifically H–bonding interactions, 2D fingerprint plots, and supramolecular architecture. The molecular simulation processes using TD–DFT/B3LYP were employed to obtain the distinguished geometry optimizations and other related parameters viz., HOMO–LUMO, molecular electrostatic potential (MEP), frequency calculations in order to support the experimental findings. Moreover, molecular docking studies have been carried out for H₂MEpheida and their corresponding Ni(II) metal complexes (1) and (2) in the active site of CAII (PDB code: 1CNX) to predict their possible interaction mode in the active site of target carbonic anhydrase II enzyme and AutoDock Vina results were further visualized and refined through receptor-ligand interactions using BIOVIA Discovery Studio 2024 program. Additionally, Tauc's equation, αhν = A(hν–E_g)r, where r = ½ for indirect and 2 for direct electronic transitions, was employed to estimate the bandgap energy (E_g) for H₂MEpheida and their corresponding Ni(II) binary and ternary complexes using UV–vis absorption data.