Structural Investigation of Asymmetrical Dimer Radical Cation System (H2O−H2S)+: Proton-Transferred or Hemi-Bonded?

Influence of the microsolvation on hemibonded and protonated hydrogen sulfide: infrared spectroscopy of [(H2S)n(X)1]+ and H+(H2S)n(X)1 (n = 1 and 2, X = water, methanol, and ethanol)

Changes of the excess charge accommodation motif in hemibonded and protonated hydrogen sulfide by microsolvation are studied by infrared spectroscopy of [(H2S)n(X)1]+ and H+(H2S)n(X)1 (n = 1 and 2, X = water, methanol, and ethanol) clusters. While the hemibond in the (H2S)2+ ion core is stable to the microhydration by a single water molecule, the hemibond is broken by the proton transfer with the microsolvation by a single methanol or ethanol molecule. Hetero hemibond formation between hydrogen sulfide and these solvent molecules is not observed. On the other hand, the excess proton in H+(H2S)n can be easily transferred to the solvent molecule, even though the proton affinity of the solvent molecule is lower than that of hydrogen sulfide. Implications of these results to the charge accommodation by sulfur under the biological conditions are discussed.

Quantum molecular motion in the mixed ion-radical complex, [(H2O)(H2S)]. Phys Chem Chem Phys 2016;18:27450-27459. [PMID: 27711703 DOI: 10.1039/c6cp05299a]

The cation dimer of water and hydrogen sulfide, [(H₂O)(H₂S)]⁺, serves as a fundamental model for the oxidation chemistry of H₂S. The known oxidative metabolism of H₂S by biological species in sulfur-rich environments has motivated the study of the inherent properties of this benchmark complex, with possible mechanistic implications for modern water oxidation chemistry. The low-energy isomer of this open-shell ion is a proton-transferred (PT) structure, H₃O⁺SH˙. An alternative PT structure, H₃S⁺OH˙, and a hemibonded (HB) isomer, [H₂O·SH₂]⁺, are also stable isomers, placing this complex intermediate to known (H₂O)₂⁺ (PT) and (H₂S)₂⁺ (HB) limiting regimes. This intermediate character suggested the possibility of unique molecular motion, even in the vibrational ground state. Path integral molecular dynamics and anharmonic vibrational spectroscopy simulations have been performed in this study, in order to understand the inherent quantum molecular motion of this complex. The resulting structural distributions were found to deviate significantly from both classical and harmonic analyses, including the observation of large-amplitude anharmonic motion of the central proton and nearly free rotation of the terminal hydrogens. The predicted vibrational spectra are particularly unique and suggest characteristic signatures of the strong electronic interactions and anharmonic vibrational mode couplings in this radical cation.

HYDROGEN SULFIDE STABILIZATION OF AN EXCESS ELECTRON ON MOLECULAR SURFACES

In the present work, a set of cyclooctane and cyclohexane molecular surfaces were used to solvate excess electrons using hydrogen sulfide ( H 2 S ). The compounds implemented have been constructed with OH groups on one side of the hydrocarbon surfaces and hydrogen atoms on the opposite side. These OH groups increased the dipole moment of systems. Simultaneously the hydrogen atoms on the opposite side of the surface for a pocket of positive charge that can attach excess electrons via dipole-bound states. The solvated anions formed between the molecular surfaces and hydrogen sulfide are stable with respect to vertical electron detachment (VDE). The effect of basis sets was also addressed in the context of VDE calculations.