Synthesis, spectroscopic studies, DFT calculations, antimicrobial and antitumor activity of tridentate NNO Schiff base metal complexes based on 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione

New Schiff base ligand was prepared by condensation of 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione with o-phenylenediamine. Cu(II), Ni(II), Co(II), VO(IV), Zn(II), Cd(II) and UO2(VI) complexes were prepared and characterized on the basis of elemental analyses, IR, (H-1 and C-13) NMR, electronic, ESR and mass spectra; magnetic, molar conductance measurements as well as thermal gravimetric analysis. The coordination sites of the Schiff base ligand are phenolic oxygen, azomethine nitrogen and amino group nitrogen; where the ligand acts as monobasic tridentate. All results established that all compounds have 1:1 (metal: ligand) stoichiometry except Ni(II)- and VO(IV)- complexes have 1:2 (metal: ligand) stoichiometry. The metal complexes showed octahedral geometry except Cu(II) complex which showed square planar arrangement and UO2(VI) has pentagonal bipyramidal arrangement. Thermodynamic parameters were calculated for the ligand and its metal complexes using Coats-Redfern method. The ligand and its complexes were tested in vitro bioassays against some Gram-negative and Gram-positive bacteria and the fungus strain; showing good results for some of these compounds. The antitumor activity of the ligand and its copper(II) and oxovanadium(IV) complexes was investigated against HepG2 cell line. Density Function Theory (DFT) level implemented in the Gaussian 09 program was used to optimize structure and some structural parameters of the ligand and its metal complexes such as: total energy, HOMO, LUMO as well as dipole moment. The computed data were correlated with the experimental results. (C) 2019 Elsevier B.V. All rights reserved.