Computational Study of the Mono- and Dianions of SO₂, SO₃, SO₄, S₂O₃, S₂O₄, S₂O₆, and S₂O₈

Abstract

DFT theory (B3LYP/6-311+G(2d)//B3LYP/6-31+G(d)) has been used to characterize sulfoxy anions and dianions as large as S2O8 2-, while post-HF theory ([QCISD(T)/6-31+G(2df)]//MP2/6-31+G(d)) has been used for systems as large as S2O3 2-. Adiabatic and vertical ionization potentials have been computed to assess the gas-phase stability of the dianions. Three dianions (S2O6 2-, S2O8 2-, and SO4 2-·4H2O) are predicted to have positive vertical ionization energies. S2O6 2- is predicted to have a negative (exothermic) adiabatic ionization potential; however, a large predicted geometry change between the dianion and monoanion rationalizes the measurable experimental lifetime of the dianion in the gas phase. Isotropic hyperfine coupling constants for 33S have been calculated for the sulfoxy monoanions and compared with experiment.

Photodetachment photoelectron spectroscopy of doubly charged anions: S2O82−

“…The structure of S 2 O 8 2Ϫ obtained from the previous DFT calculations is also given. 20 The average distance between the terminal O atoms, where the negative charges are most likely localized, is estimated to be about 4.8 Å. Using Coulomb's law (e 2 /4⑀ 0 r) and this average charge separation distance, we estimated an intramolecular Coulomb repulsion of ϳ3 eV, which is consistent with the above estimate of the RCB.…”

“…Apparently, the previously calculated EBa ͑0.35 eV͒ using DFT was too low. 20 We noted that the X feature in the 266 nm spectrum exhibited a shift to lower binding energy relative to that at 193 nm by about 0.1 eV. As we have shown previously, 18 such a spectral shift was due to electron tunneling through the RCB, suggesting that even the 266 nm photon energy was below the RCB relative to the ground state.…”

“…22 Several exothermic dissociation channels have been calculated in the previous DFT study. 20 Collisional induced dissociations of S 2 O 8 2Ϫ have been experimentally observed. 10 All the dissociation processes involved formation of two singly charged anions.…”

“…10 It has also been studied theoretically with density functional theory ͑DFT͒ and positive electron binding energies were obtained, confirming its stability as a free dianion. 20 We measured the PES spectra of S 2 O 8 2Ϫ at three photon energies: 193, 266, and 355 nm and determined its electron binding energies. We show how the PES spectra are affected by the RCB and the electron tunneling effects.…”

Theoretical Study of Intermediates in the Urate Oxidase Reaction

“…The calculations suggest that removal of a single electron from urate dianion in the gas phase is thermodynamically favorable, while the electron is relatively strongly bound in urate monoanion and in uric acid. The analyses of dianions that are unstable with respect to electron autodetachment require special care since a sufficiently flexible method could give the radical anion and a free electron as the lowest energy solution (41). Use of standard diffuse functions has been shown to provide unreliable energy and structural parameters for some unstable dianions (42).…”