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Computational Electrochemistry: The Aqueous Ru³⁺|Ru²⁺ Reduction Potential

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Pablo Jaque, Aleksandr V. Marenich, Christopher J. Cramer,* and Donald G. Truhlar*

Department of Chemistry and Supercomputing Institute, 207 Pleasant Street SE, University of Minnesota, Minneapolis, Minnesota 55455-0431

J. Phys. Chem. C, 2007, 111 (15), pp 5783–5799

DOI: 10.1021/jp066765w

Publication Date (Web): March 28, 2007

E-mail: cramer@chem.umn.edu (C.J.C.); truhlar@chem.umn.edu (D.G.T.).

Abstract

We present results of density functional calculations for the standard reduction potential of the Ru³⁺|Ru²⁺ couple in aqueous solution. The metal cations are modeled as [Ru(H₂O)_n]^q⁺ surrounded by continuum solvent (q = 2, 3; n = 6, 18). The continuum model includes bulk electrostatic polarization as well as atomic surface tensions accounting for the deviation of the second or third hydration shell from the bulk. After consideration of 37 density functionals with 5 different basis sets, it has been found that hybrid and hybrid meta functionals provide the most accurate predictions for the [Ru(H₂O)_n]^q⁺ geometries and for the corresponding reduction potential in comparison with available experimental data. The gas-phase ionization potentials of [Ru(H₂O)_n]²⁺ calculated by density functional theory are also compared to results of ab initio computations using second-order Møller−Plesset perturbation theory. The difference in solvation free energies of Ru³⁺ and Ru²⁺ varies from −10.56 to −10.99 eV for n = 6 and from −6.83 to −7.45 eV for n = 18 depending on the density functional and basis set quality. The aqueous standard reduction potential is overestimated when only the first solvation shell is treated explicitly and is underestimated when the first and second solvation shells are treated explicitly.

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History

Published In Issue April 19, 2007
Received October 14, 2006
Revised January 16, 2007

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Article

Computational Electrochemistry: The Aqueous Ru³⁺|Ru²⁺ Reduction Potential