Synthesis and physicochemical studies of metal complexes of some new Shciff bases containing 1,3-thiazine-2,6(3H)-dione

Abstract

A large number of Schiff base ligand and their metal complexes have been studied because of their interesting and important properties. 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione (AHTD), and their corresponding Schiff base ligands and their metal complexes have been studied. This field increased considerably because of the attractive observation that different ligands show different biological properties including antifungal, antibacterial, antimalarial, antitumoral, antiviral and antioxidant activities. For these applications, we are extending this field in synthesis of novel Schiff base complexes. In the present work, the Schiff base ligands were prepared by the condensation of 5-acetyl-4-hydroxy-2H-1,3-thiazine-2,6(3H)-dione (AHTD) as starting material, with in the molar ratio 1:1 to afford the corresponding Schiff base ligands; H2La, H2Lb, and H2LC respectively. The structures of the ligands were elucidated by elemental analyses, IR, mass, 1H-NMR and electronic spectra. Molecular orbital calculations of the ligands were obtained using hyperchem 7.5 program. The reactions of these Schiff base ligands with copper(II), nickel(II), cobalt(II), cadmium(II), zinc(II), iron(III), chromium(III), cerium(III), vanadyl(IV) and uranyl(IV) ions in a molar ratio (1:1, ligand: metal ion) were studied. All reactions afforded monomeric complexes. The newly prepared metal complexes of these ligands were identified by elemental analyses, infrared, electronic, mass, 1H-NMR and ESR spectra as well as magnetic susceptibility measurements, molar conductance and thermal gravimetric (TGA) analysis. Copper(II), nickel(II), cobalt(II), vanadyl(IV), iron(III), chromium(III), zinc(II), cadmium(II) and uranyl(IV) complexes exhibit an octahedral geometry, except copper(II) and vanadyl(IV) complexes give square pyramidal geometry, nickel(II) complex exhibit a square planar geometry, cerium(III) and uranyl(IV) exhibit octa-coordinated around metal ion for H2La ligand. Cerium(III) and uranyl (IV) exhibit pentagonal bipyramid around metal ion for H2Lb ligand. The Schiff base ligands behave as dibasic or monobasic tetradentate and pentadentate chelating sites via azomethine nitrogen, phenolic oxygen atoms for H2La and H2Lb and chelating sites via azomethine nitrogen, phenolic oxygen atoms and amino group for H2Lc Thermal gravimetric analysis (TGA) was performed for some complexes of each ligand. Thermodynamic parameters (ΔG, ΔH, ΔS and Ea) of the metal complexes were calculated using Coats-Redfern method and standard thermodynamic equations, and this was performed using the thermal degradation of the solid complexes using TGA curves. Molecular modeling carried out for the free ligands and its complexes and the theoretical results were correlated with the experimental data. The ligand and its metal complexes were screened for their antimicrobial activity against Staphylococcus aureus and Bacillus subtilis as Gram-positive bacteria, Escherichia coli and Salmonella typhimurium as Gram-negative bacteria, Candida albicans and Aspergillus fumigatus as fungal strains.