Steric effects in electron-transfer reactions. 3. Use of electrochemically measured diffusion coefficients to estimate the average radii of transition-metal complexes

Carl A. Koval, Michael E Ketterer, Cindy M. Reidsema

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Abstract

The estimation of van der Waals radii for transition-metal complexes is critical for comparison of the electron-transfer reactivity of these molecules with theoretical predictions. Presently, these radii are usually estimated with X-ray crystallography and/or molecular models. When the complexes are not spherical or when the ligand structure has large voids, these estimates may not accurately represent the true average radius. We report the diffusion coefficients for a variety of transition-metal complexes in aqueous solutions containing low concentrations (0.05-0.12 M) of 1:1 electrolytes. The diffusion coefficients, D, were measured electrochemically by utilizing a rotating glassy-carbon-disk electrode. Most of the complexes examined constitute structurally related redox series in which the complexes differ only in the size of the organic substituents bound to the ligands. The uncorrected diffusion coefficients range from 2.2 × 10-6 to 8.3 × 10-6 cm2 s-1, while the average radii, 〈r〉, estimated from models range from 3.4 to 9.1 Å. The use of the diffusion coefficients to calculate limiting ionic conductivities and average radii is discussed.

Original languageEnglish (US)
Pages (from-to)4201-4205
Number of pages5
JournalJournal of Physical Chemistry
Volume90
Issue number17
StatePublished - 1986
Externally publishedYes

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Coordination Complexes
Metal complexes
Transition metals
electron transfer
diffusion coefficient
transition metals
radii
Electrons
estimates
Ligands
X ray crystallography
Glassy carbon
Ionic conductivity
ligands
Electrolytes
glassy carbon
ion currents
crystallography
voids
low concentrations

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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title = "Steric effects in electron-transfer reactions. 3. Use of electrochemically measured diffusion coefficients to estimate the average radii of transition-metal complexes",
abstract = "The estimation of van der Waals radii for transition-metal complexes is critical for comparison of the electron-transfer reactivity of these molecules with theoretical predictions. Presently, these radii are usually estimated with X-ray crystallography and/or molecular models. When the complexes are not spherical or when the ligand structure has large voids, these estimates may not accurately represent the true average radius. We report the diffusion coefficients for a variety of transition-metal complexes in aqueous solutions containing low concentrations (0.05-0.12 M) of 1:1 electrolytes. The diffusion coefficients, D, were measured electrochemically by utilizing a rotating glassy-carbon-disk electrode. Most of the complexes examined constitute structurally related redox series in which the complexes differ only in the size of the organic substituents bound to the ligands. The uncorrected diffusion coefficients range from 2.2 × 10-6 to 8.3 × 10-6 cm2 s-1, while the average radii, 〈r〉, estimated from models range from 3.4 to 9.1 {\AA}. The use of the diffusion coefficients to calculate limiting ionic conductivities and average radii is discussed.",
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year = "1986",
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T1 - Steric effects in electron-transfer reactions. 3. Use of electrochemically measured diffusion coefficients to estimate the average radii of transition-metal complexes

AU - Koval, Carl A.

AU - Ketterer, Michael E

AU - Reidsema, Cindy M.

PY - 1986

Y1 - 1986

N2 - The estimation of van der Waals radii for transition-metal complexes is critical for comparison of the electron-transfer reactivity of these molecules with theoretical predictions. Presently, these radii are usually estimated with X-ray crystallography and/or molecular models. When the complexes are not spherical or when the ligand structure has large voids, these estimates may not accurately represent the true average radius. We report the diffusion coefficients for a variety of transition-metal complexes in aqueous solutions containing low concentrations (0.05-0.12 M) of 1:1 electrolytes. The diffusion coefficients, D, were measured electrochemically by utilizing a rotating glassy-carbon-disk electrode. Most of the complexes examined constitute structurally related redox series in which the complexes differ only in the size of the organic substituents bound to the ligands. The uncorrected diffusion coefficients range from 2.2 × 10-6 to 8.3 × 10-6 cm2 s-1, while the average radii, 〈r〉, estimated from models range from 3.4 to 9.1 Å. The use of the diffusion coefficients to calculate limiting ionic conductivities and average radii is discussed.

AB - The estimation of van der Waals radii for transition-metal complexes is critical for comparison of the electron-transfer reactivity of these molecules with theoretical predictions. Presently, these radii are usually estimated with X-ray crystallography and/or molecular models. When the complexes are not spherical or when the ligand structure has large voids, these estimates may not accurately represent the true average radius. We report the diffusion coefficients for a variety of transition-metal complexes in aqueous solutions containing low concentrations (0.05-0.12 M) of 1:1 electrolytes. The diffusion coefficients, D, were measured electrochemically by utilizing a rotating glassy-carbon-disk electrode. Most of the complexes examined constitute structurally related redox series in which the complexes differ only in the size of the organic substituents bound to the ligands. The uncorrected diffusion coefficients range from 2.2 × 10-6 to 8.3 × 10-6 cm2 s-1, while the average radii, 〈r〉, estimated from models range from 3.4 to 9.1 Å. The use of the diffusion coefficients to calculate limiting ionic conductivities and average radii is discussed.

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