Sulfonamide derived Schiff base Mn (II), Co (II), and Ni (II) complexes: Crystal structures, density functional theory and Hirshfeld surface analysis

The three transition metal complexes of the ligand named as 2,4‐dibromo‐6‐{[2‐(1,1‐dioxo‐1H‐benzoisothiazole‐3‐yl‐amino)‐ethylimino]‐methyl}‐phenol 3 were synthesized with divalent manganese, cobalt and nickel metal ions and characterized by employing different analytical methods including UV–visible, FT‐IR and elemental analyses. The crystal structures of Mn (II) complex 4, Co (II) complex 5, and Ni (II) complex 6 are determined by single beam X‐rays crystallography, which confirm the distorted octahedral coordination of the complexes 4–6. The non‐covalent interactions of the complexes 4–6 are investigated by the Hirshfeld surface analysis. The tendency of the pair of chemical species to form crystal packing interactions are computed, which provide the favorable contacts in the crystal packing for the complexes 4–6. For the sake of computing strength of the crystal packing, void analysis is performed for the complexes 4–6. The non‐electrolytic nature of synthesized metal complexes was confirmed by molar conductance. The spectral analyses suggested that sulfonamide functionalized Schiff base behaves as bidentate ligand and coordinates with the metal center through phenolic oxygen and iminic nitrogen atoms. The density functional theory (DFT) studies were performed for the Mn (II), Co (II), and Ni (II) metal complexes at the B3LYP/LANL2DZ level of theory. The structural characteristics, vibrational analysis (IR), NMR analysis, UV–Vis, natural bonding orbital (NBO), frontier molecular orbital (FMO), charges (Mulliken and NPA), global reactivity descriptors, molecular electrostatic potential (MEP), and dipole moments were investigated using this method. The large values of stabilization energy, that is, 12.02, 15.25, and 23.81 kcal/mol were found for the complexes Mn (II) 4, Co (II) 5, and Ni (II) 6, respectively by NBO analysis. The global reactivity findings suggested the positive values of electron affinity for all complexes, which indicate the involvement of charge transfer reaction. Among these complexes, complex 6 is the most stable and complex 4 is the least. Further, FMO analysis indicated large HOMO‐LUMO gap (3.85–3.97 eV) with higher LUMO values for all metal complexes.