On The Nature of FeIV=Oaq in Aqueous Media: A DFT analysis

Abstract

AbstractFeIV=Oaq is a key intermediate in many advanced oxidation processes and probably in biological systems. It is usually referred to as FeIV=O2+. The pKa's of FeIV=Oaq as derived by DFT are: pKa1=2.37 M06 L/6‐311++G(d,p) (SDD for Fe) and pKa2=7.79 M06 L/6‐311++G(d,p) (SDD for Fe). This means that in neutral solutions, FeIV=Oaq is a mixture of (H2O)4(OH)FeIV=O+ and (H2O)2(OH)2FeIV=O. The oxidation potential of FeIV=Oaq in an acidic solution, E0{(H2O)5FeIV=O2+/FeIII(H2O)63+, pH 0.0} is calculated with and without a second solvation sphere and the recommended value is between 2.86 V (B3LYP/Def2‐TZVP, with a second solvation sphere) and 2.23 V (M06 L/Def2‐TZVP without a second solvation sphere). This means that FeIV=Oaq is the strongest oxidizing agent formed in systems involving FeVIO42− even in neutral media.