Solution properties of iron(III) complexes with 5-fluorosalicylic acid — spectra, speciation, and redox stability

Abstract

The iron(III)-5-fluorosalicylic acid systems were investigated in water by pH potentiometry combined with UV-VIS spectrophotometry. The data revealed that stable aquated mono-, bis-, and tris(5-fluorosalicylato) iron(III) complexes are formed, together with their monohydroxo and dihydroxo analogues. The stability constants of all present iron(III) species were calculated. Based on pH and metal:ligand ratio dependent distribution of the species, electronic absorption spectra of the complexes in the visible region were obtained. Redox stability was monitored as an ability to undergo both spontaneous and photoinduced reduction of Fe(III) to Fe(II). Complexes do not undergo any redox changes when in the dark both in methanol or water. While aqueous solutions of 2 complexes are stable under the influence of incident visible radiation, steady-state irradiation of the methanolic systems by visible light led to the photoreduction of Fe(III) to Fe(II), the quantum yield of the Fe(II) photoformation was determined.