Iron(III) complexes with N⁴-para-tolyl-thiosemicarbazones: spectral and electrochemical studies and toxicity to Artemia salina

Abstract

Iron(III) complexes [Fe(H2Fo4pT)Cl₃] (1), [Fe(H2Ac4pT)Cl₃] (2) and [Fe(H2Bz4pT)Cl₃] (3) with N⁴ -para-tolyl-thiosemicarbazones derived from 2-formyl (H2Fo4pT), 2-acetyl (H2Ac4pT) and 2-benzoylpyridine (H2Bz4pT) were prepared and characterized. EPR data for 1–3 reveal the presence of low-spin iron(III) with d _xz ²d _yz ²d _xy ¹ ground state. Electrochemical studies of the complexes showed mostly metal-centered redox changes with a quasi-reversible Fe(III)/Fe(II) couple. H2Fo4pT and H2Ac4pT exhibited toxicity against Artemia salina at low doses (LD₅₀ = 27.5 µM and LD₅₀ = 4.7 µM, respectively). Upon coordination the toxicity increased substantially in the case of [Fe(H2Fo4pT)Cl₃] (LD₅₀ = 1.9 µM) and did not change for [Fe(H2Ac4pT)Cl₃]. H2Bz4pT and its iron(III) complex were not soluble in water.

Keywords:

• N ⁴-para-tolyl-thiosemicarbazones
• Iron(III) complexes
• EPR spectra
• Electrochemistry
• Artemia salina

Acknowledgements

This work was supported by CNPq and Instituto do Milênio-Inovação e Desenvolvimento de Novos Fármacos e Medicamentos (IM-INOFAR, Proc. CNPq 420015/05-1). We thank the Centro Brasileiro de Pesquisas Físicas (CBPF) and Prof. Eliane Wajnberg for the accessibility and assistance with the EPR spectrometer.