Reductions of oxygen, carbon dioxide, and acetonitrile by the magnesium(II)/Magnesium(I) couple in aqueous media : Theoretical insights from a nano-sized water droplet

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

6 Scopus Citations
View graph of relations

Author(s)

Detail(s)

Original languageEnglish
Pages (from-to)2780-2792
Journal / PublicationJournal of Physical Chemistry A
Volume119
Issue number12
Publication statusPublished - 26 Mar 2015

Abstract

Reductions of O2, CO2, and CH3CN by the half-reaction of the Mg(II)/Mg(I) couple (Mg2+ + e- → Mg+•) confined in a nanosized water droplet ([Mg(H2O)16]•+) have been examined theoretically by means of density functional theory based molecular dynamics methods. The present works have revealed many intriguing aspects of the reaction dynamics of the water clusters within several picoseconds or even in subpicoseconds. The reduction of O2 requires an overall doublet spin state of the system. The reductions of CO2 and CH3CN are facilitated by their bending vibrations and the electron-transfer processes complete within 0.5 ps. For all reactions studied, the radical anions, i.e., O2 •-, CO2 •-, and CH3CN•-, are initially formed on the cluster surface. O2 •- and CO2 •- can integrate into the clusters due to their high hydrophilicity. They are either solvated in the second solvation shell of Mg2+ as a solvent-separated ion pair (ssip) or directly coordinated to Mg2+ as a contact-ion pair (cip) having the 1n-[MgO2]•+ and 1n-[MgOCO]•+ coordination modes. The 1n-[MgO2]•+ core is more crowded than the 1n-[MgOCO]•+ core. The reaction enthalpies of the formation of ssip and cip of [Mg(CO2)(H2O)16]•+ are -36 ± 4 kJ mol-1 and -30 ± 9 kJ mol-1, respectively, which were estimated based on the average temperature changes during the ion-molecule reaction between CO2 and [Mg(H2O)16]•+. The values for the formation of ssip and cip of [Mg(O2)(H2O)16]•+ are estimated to be -112 ± 18 kJ mol-1 and -128 ± 28 kJ mol-1, respectively. CH3CN•- undergoes protonation spontaneously to form the hydrophobic [CH3CN, H]. Both CH3CN and [CH3CN, H] cannot efficiently penetrate into the clusters with activation barriers of 22 kJ mol-1 and ∼40 kJ mol-1, respectively. These results provide fundamental insights into the solvation dynamics of the Mg2+/Mg•+ couple on the molecular level.

Citation Format(s)

Reductions of oxygen, carbon dioxide, and acetonitrile by the magnesium(II)/Magnesium(I) couple in aqueous media : Theoretical insights from a nano-sized water droplet. / Lam, Tim-Wai; Zhang, Han; Siu, Chi-Kit.

In: Journal of Physical Chemistry A, Vol. 119, No. 12, 26.03.2015, p. 2780-2792.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review