Fabrication of novel Fe (III), Co (II), Hg (II), and Pd (II) complexes based on water-soluble ligand (NaH2PH): structural characterization,cyclic voltammetric,powder X-ray diffraction,zeta potential,and biological studies

Sodium4-hydroxy-3-(2-picolinoylhydrazineylidene]methyl)benzenesulfonate (NaH₂PH) was synthesized as a novel water-soluble ligand, by the condensation of picolinohydrazide with sodium 3-formyl-4-hydroxybenzenesulfonate. The (NaH₂PH) ligand and its isolated Co (II), Fe (III), Hg (II), and Pd (II) complexes were analyzed by elemental analysis and characterized by spectroscopic (Fourier transform infrared spectroscopy, UV–visible, powder XRD, ¹H NMR,¹³C NMR, MS) and magnetic measurements. By comparing IR spectra of both ligand and the metal complexes, one can assume that the (NaH₂PH) ligand behaves as a bi-negative tetradentate (ONNO) in Co (NaPH)(H₂O)₂].3H₂O, and a mono-negative tridentate (ONO) in Fe (NaPH)Cl₂(H₂O)] complex, whereas in Hg₂(NaPH)Cl₂(H₂O)] complex, (NaH₂PH) coordinates as a bi-negative pentadentate (ONNNO) ligand via deprotonated OH group of phenolic ring (C=N)_Py and (C=N*) coordinated to one of Hg (II) ion and the oxygen atom of enolic group and (C=N)_az group with the another Hg (II) ion. Moreover, (NaH₂PH) acts as bi-negative tridentate (ONO) ligand in Pd (NaPH)(H₂O)].2H₂O complex. The geometries of complexes were suggested based on the UV–visible spectra, magnetic measurements and confirmed by applying discrete Fourier transform (DFT) optimization studies. The thermal fragmentation of both Pd (NaPH)(H₂O)].2H₂O and Co (NaPH)(H₂O)₂].3H₂O complexes was performed, and the kinetic and thermodynamic parameters were computed using the Coats–Redfern and Horowitz–Metzger methods. The redox behavior of divalent ions of cobalt and mercury were discussed by the cyclic voltammetry technique in the presence and absence of (NaH₂PH) ligand. Biological potencies of the ligand and its metal complexes were evaluated as antioxidants (ABTS and DPPH), anticancer, DNA, and antimicrobial (Staphylococcus aureus and Bacillus subtilis as Gram (+) bacteria, Escherichia coli and Pseudomonas aeruginosa as Gram (?) bacteria, and Candida albicans as fungi).