Study in Aqueous Solutions of Bioactive 2-Pyridineformamide-Derived Thiosemicarbazones and Their Iron(II) and Iron(III) Complexes

• Published in: Journal of solution chemistry Vol. 42; no. 3; pp. 555 - 565
• Main Authors: Vilhena, Felipe S., Teixeira, Letícia R., Alves, Odivaldo Cambraia, Beraldo, Heloisa, da S. Miranda, Fabio, Felcman, Judith
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.03.2013
• Subjects: Aqueous solutions; Binary systems; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Constants; Derivatives; Geochemistry; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Ligands; Mathematical analysis; Oceanography; Physical Chemistry; Spectra; Stability constants; Iron complexes; 2-Pyridineformamide thiosemicarbazones; EPR spectroscopy
• ISSN: 0095-9782; 1572-8927
• DOI: 10.1007/s10953-013-9977-x

The binary systems of iron(II) and iron(III) with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N (4)-methyl (H2Am4Me), N (4)-ethyl (H2Am4Et) and N (4)-phenyl (H2Am4Ph) derivatives were studied in aqueous solution by pH-potentiometry, ultraviolet–visible spectroscopy and EPR spectra. The formation constants of the iron(II) and iron(III) complexes were calculated from potentiometric and electronic absorption data at 25 °C and ionic strength μ  = 0.1 mol·L −1 using the HYPERQUAD program. The values of the formation constant of the FeL species decrease in the order Fe:H2Am4DH > Fe:H2Am4Me ≈ Fe:H2Am4Et > Fe:H2Am4Ph in the same way as the basicity of the ligands. The species distribution diagrams show that the species FeL 2 predominates at physiological pH in the Fe:H2Am4DH, Fe:H2Am4Me and Fe:H2Am4Et systems. The similar EPR spectra of these iron(III) binary systems indicate the same coordination spheres around the metallic center and the EPR g values suggests that the unpaired electron is in the d xy orbital, indicating a d xz 2 d yz 2 d xy 1 ground state configuration for the complexes. For the Fe(III):H2Am4Ph system the EPR results indicated dimerization and antiferromagnetic interaction due to the presence of only one thiosemicarbazone ligand around the metallic center.