(i) an oxo band comprised of occupied oxo ligands; (ii) and a metallic band encompassing unoccupied addenda orbitals. Figure depicts the frontier molecular orbitals (FMOs) of [M(H2O)PW11O39] q-, and Wells-Dawson, [M(H2O)P2W17O61] q-anions, in aqueous solution. It can be found that the newly incorporated orbitals are inserted between the occupied oxo-and unoccupied addenda band. The molecular orbital diagrams shown in Figure and SI-1 were optimized using PBE/TZP for all Keggin, [M(H2O)PW11O39] q-and Wells-Dawson, [M(H2O)P2W17O61] q-anions. Standard reduction potentials, U 0 red vs SHE, were determined using four different exchange and correlation functionals to examine the effect of increasing levels of Hartree-Fock exchange. In previous work, cathodic reduction of POMs have been estimated using the energy difference between the one-electron reduced and oxidized formsthe reduction energy (RE). An electron addition to a nonbonding orbital means the entropic and vibrational contributions to ΔG can be replaced by its electronic contribution in solution. However, one-electron reductions of Keggin, [M(H2O)PW11O39] q-, anions, in particular for Mn(III/II) and Co(III/II) redox couples, significantly distort the inner coordination sphere at the peripheral heteroatom. Therefore, total Gibbs free energy was computed for each system to account for integral entropic and vibrational contributions. Generally, reduction potentials were overestimated, regardless of the model selectedsee Table . A notable exception to this was observed for PBE0 / TZP methodology calculating aa potential of 1.52 V vs SHE. Analysis of