Synthesis, characterization, crystal structure, theoretical studies, and antibacterial activities of P-coordinated mercury(II) complexes containing phosphine–phosphonium salts

Abstract

The reaction of mercury(II) halides with the phosphine–phosphonium salts [PPh2(CH2)2PPh2CH2C(O)C6H4R]Br (R=Br (S1), NO2 (S2) in methanol affords the zwitterionic mercury(II) complexes {HgX2Br(PPh2(CH2)2PPh2CH2C(O)C6H4R)} [R=Br: X=Cl (1), Br (2), I (3); R=NO2: X=Cl (4), Br (5), I (6)]. These complexes were fully characterized by elemental analysis and spectroscopic techniques such as IR, 1H, 31P, and 13C NMR. The structure of complex 4 has been characterized crystallographically. Single crystal X-ray analysis reveals the presence of mononuclear P-coordinated complex containing Hg(II) in a distorted tetrahedral environment. Theoretical studies using density functional theory have been performed on the free ligands (S1 and S2) and their corresponding complexes (1–6). Electronic and structural properties of latter compounds were examined and general trends were derived. The natural bonding orbital calculations have also been carried out to understand the nature of the Hg–P bond. The results show that the interactions between the metal atom and phosphorus atom of phosphine group are mainly an electrostatic interaction. In addition, there is a decrease in the charge distribution on the ligand reflecting electron transfer from the ligand to the metal and halogens atoms. The in vitro antibacterial activities of the entitled compounds were evaluated against Gram-negative as Escherichia coli and Pseudomonas aeruginosa bacteria and Gram-positive as Bacillus subtilis and Staphylococcus aureus and compared with the standard antibacterial drugs.