Graphical abstractSynthesis, spectroscopic, coordination and biological activities of some organometallic complexes derived from thio-Schiff base ligands

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A hydrazone Schiff base ligand was synthesized by the condensation of 3-formyl-4-hydroxycoumarin and oxalyldihydrazide in the molar ratio 2:1. The Schiff base ligand acts as a mono-, bi-, tri- or even tetradentate ligand with metal cations in the molar ratios 1:1 or 2:1 (M:L) to yield either mono- or binuclear complexes as keto or enol isomers, where M = Co(II), Ni(II), Cu(II), VO(IV), and Fe(III). The ligand and its metal complexes were characterized by elemental analyses, IR, 1H NMR, mass, and UV–Vis spectroscopy. Furthermore, the magnetic moments were calculated from the measured electric conductivities of the complexes. According to the received data, the dihydrazone ligand contains one or two units of ONO domains and can bind to the metal ions via the azomethine nitrogen, the carbonyl oxygen atoms, and/or the phenolic oxygen atoms. Electronic spectra and the magnetic moments of all complexes show that the complexes’ geometries are either octahedral, tetrahedral, square planar, or square pyramidal. Cyclic voltammograms of the mononuclear Co(II) and Ni(II) complexes show quasi-reversible peaks. Tests against two pathogenic bacteria as Gram-positive and Gram-negative bacteria for both, the Schiff base ligand and its metal complexes were carried out. In addition, also one kind of fungi was tested. The synthesized complexes demonstrate mild antibacterial and antifungal activities against these organisms.Graphical abstract Electronic supplementary materialThe online version of this article (doi:10.1007/s00706-017-2075-9) contains supplementary material, which is available to authorized users.

In this elucidation, the reactivity of isonicotinohydrazide derivative (3)(L) was reacted with the nitrate salts of Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Zn(II) to afford the corresponding stable metal coordination compounds. The synthesized metal coordination compounds were confirmed through physicochemical and analytical analysis such as elemental analysis, UV‐Visible, FT‐IR, TGA, Mass, 1H NMR, XRD, magnetic, and molar conductance analysis. All complexes exhibit distorted octahedral geometry except Zn(II) complex which has a distorted tetrahedral arrangement. Both the thermal stability and the kinetic parameter for all complexes were elucidated via TGA analysis and Coats‐Redfern method. XRD study suggested that the complexes have a partially amorphous structure which was further confirmed by calculating the crystallinity index. Moreover, the synthesized metal complexes exhibited excellent cytotoxicity  activity contra lung cancer cells (A549) and liver cancer cells (HepG2) using neutral red uptake assay. The complexes of Fe(III), Ni(II), and Zn(II) showed higher cytotoxic effect than doxorubicin against A549 and HepG2 cells for 24 h incubation. Furthermore, the Cr(III), Co(II), Zn(II), and Cu(II) coordination compounds showed more inhibitory influence when treated with A549 and HepG2 cells for 48 h incubation. The biological studies of these complexes were confirmed through molecular docking studies with different proteins such as (PDB ID: 2ITO) and (PDB ID: 5H38) and showed low binding energy and shortage bond length with different amino acids. Also, computational calculations of all metal complexes were carried out utilizing DFT/B3LYP/LANL2DZ basis set to detect the FMO, ESP, MEP, and physical descriptor's of them and confirms their reactivity.