Synthesis and characterization of thorium (IV) complexes of 2-aminothiazole and their evaluation as effective antimicrobial and antioxidant agents

Two novel Th(IV) complexes [Th(L 1 ) 2 (NO 3 ) 3 ]NO 3 ·6H 2 O and [Th(L 2 ) 2 (NO 3 ) 3 ]NO 3 ·6H 2 O have been prepared by reaction between nitrate salt of thorium and bidentate Schiff base ligands 2,3-dihydro-1H-indolo[2,3-b]phenazine-4(5H)-ylidene)thiazole-2-amine (L 1 ), and N-(3-(ethoxymethylene)-2,3-dihydro-1H-indolo[2,3-b]phenazine-4(5H)-ylidene)thiazole-2-amine (L 2 ). The compounds were characterized by FTIR, 1 H NMR, UV-Vis spectroscopy, magnetic susceptibility, and molar conductivity. The structures of the complexes were determined by powder XRD pattern. Elemental analysis of ligands and their complexes are well agreed with the proposed formulae. The powder XRD pattern of the complexes showed cubic crystal structure. Moreover, the thermal behavior of the complexes was investigated in the range 30-600 °C, and the results showed that the ligand absolutely decomposed, however the thorium complexes leave metallic thorium oxide as a final residue. The ability of these compounds to inhibit the growth of pathogenic organisms Bacillus subtilis, Staphylococcus aureus (Gram-positive bacteria), Escherichia coli (Gram-negative bacteria), Candida tropicalis (yeast) and Aspergillus niger (fungal species) were compared to known antibiotics amoxicillin. In vitro antioxidant scavenging activity was determined according to the elimination of radicals from 2-diphenyl-1-picrylhydrazyl (DPPH) and H 2 O 2 .