Density functional theory calculation of μ-oxo and μ-hydroxo bridged iron(III) aqua dimer complexes in perfluorinated sulfonic acid ionomer membranes

Spectroscopic properties of diiron(III) decahydrates in iron(III) exchanged Nafion membranes were calculated by DFT method. Optimized geometries, quadrupole splitting constants in Mossbauer spectra, vibrational frequencies and electronic transition energies of mu-oxo diiron(III) decahydrate calculated with range-separated hybrid functionals were in excellent agreement with the experimental values. Another doublet species observed in Mossbauer spectra was identified as mu-hydroxo diiron(III) decahydrate, which has been hitherto assigned as a hydrogen peroxide bridged dimer. Changes in relative abundance of mu-oxo and mu-hydroxo complexes by protonation/deprotonation of the diiron(III) decahydrates were explained by relative abundance and stability of hydrated protons in iron(III) exchanged Nafion membranes. (C) 2015 Elsevier B.V. All rights reserved.