A Car-Parrinello study of the formation of oxidizing intermediates from Fenton's reagent in aqueous solution

Abstract:

This chapter demonstrates the spontaneous formation of the much contested ferryl ion, Fe $^{\mathrm{IV}}$O$^{2+}$, in an aqueous solution of iron(II) and hydrogen peroxide by means of first principles molecular dynamics simulations. Starting from hydrogen peroxide coordinated to pentaaqua iron(II) in water, we show that the oxygen-oxygen bond breaks spontaneously to form [(H$_2$O)$_5$Fe $^{\mathrm{III}}$OH]$^{2+}$ and a very short living OH. radical. This radical abstracts immediately a hydrogen from a water ligand to form [(H$_2$O)$_4$Fe $^{\mathrm{IV}}$(OH)$_2$]$^{2+}$ and a water molecule. The hydrated ferryl ion [(H$_2$O)$_5$Fe $^{\mathrm{IV}}$O]$^{2+}$ is formed in a second step by proton donation from one OH ligand to the solvent. Starting from separated hydrogen peroxide and pentaaqua iron(II) in water, we find a reactive pathway in which the ferryl ion is formed in a more direct way. As soon as H$_2$O$_2$ enters the iron(II) coordination shell, the oxygen-oxygen bond breaks and again an OH ligand and a short living OH. radical is formed. The radical abstracts the hydrogen from the OH ligand to form again the ferryl ion.