Crystal structure and antibacterial activity of the novel octahedral [Ni(DPPMO₂)₃]CL₂.H₂O : synthesis, characterization, and computational studies

The aim of the present study is to synthesize a novel nickel (II) complex containing dppmO2 as a ligand. By refluxing a solution of nickel (II) salt with 1,1-bis(diphenylphosphino)methane (dppm) in a molar ratio of 1:3 in mixed solvents methanol (CH₃OH) and dichloromethane (CH₂Cl₂), a green solid of Ni(II) complex was yielded. The reaction resulted in the oxidation of the phosphine ligand and formation of the octahedral structure of the tris-doubly-oxygenated Ni(II) complex [Ni(dppmO2)3]Cl2. H2O, with dppmO₂ as the phosphine oxide derivative dppmO2. Using molar conductivity and various spectroscopic methods, including FTIR, UV-Vis, and single crystal X-ray diffraction, confirming crystallization in a triclinic system with a P-1 space group. Theoretical investigations, such as DFT, non-covalent interaction analysis, and molecular electrostatic potential (MEP) mapping, were conducted on the synthesized complex. The findings indicate that the free dppm ligand exhibits a wider energy gap (ΔE = 6.4166 eV), making it more stable and less reactive than the nickel complex (3.28 eV). Furthermore, both the dppm ligand and its nickel complex were evaluated for antibacterial properties, revealing that the nickel complex demonstrates no inhibitory effect against Staphylococcus aureus, but it shows stronger inhibitory effect against Escherichia coli compared to the free ligand. KEY WORDS: Crystal structure, DFT calculations, dppmO2 ligand, Nickel(II) complex, Hirshfeld surface analysis Bull. Chem. Soc. Ethiop. 2026, 40(4), 779-794. DOI: https://dx.doi.org/10.4314/bcse.v40i4.5