Facile Determination of the Spectra of Unstable Electrode Products Using Simultaneous Fiber-Optic Chronoabsorptometry and Chronoamperometry

Abstract

A widely applicable fiber-optic UV-vis method to determine the spectra of in situ generated redox products and intermediates at or near an electrode surface is described mathematically and implemented experimentally. The quantitative spectral information obtained gives extinction coefficients (absorptivities) as a function of wavelength, requires no arbitrary subtraction of the spectrum of the starting material, and is relatively insensitive to path length and concentration during the spectroelectrochemical measurements. We demonstrate proof-of-concept of this methodology by reproducing the expected spectrum of the ferrocenium ion from electrooxidation of ferrocene in MeCN, and by reproducing the spectrum that reveals π-radical cation formation from the electrooxidation of (T(p-OMe)PP)Co(NO) ((T(p-OMe)PP = 5,10,15,20-tetra(p-methoxyphenyl)porphyrinato dianion). Importantly, we demonstrate its use for the facile detection of unstable redox products not previously detected by current spectroelectrochemical methods. We obtain, for the first time, the experimental UV-vis spectrum of the short-lived fac-[(dppe)Mn(CO)(3)Br](+) cation, a hitherto uncharacterized intermediate that forms during the archetypal redox-induced fac-to-mer isomerization of (dppe)Mn(CO)(3)Br (dppe = diphenylphosphinoethane). Spectral features of the Mn-containing species have been verified by comparison to theoretical spectra calculated by time-dependent density functional theory methods.

Electrochemical Investigation of the Kinetics of Chloride Substitution upon Reduction of [Ru(porphyrin)(NO)Cl] Complexes in Tetrahydrofuran

“…General synthetic and electrochemical procedures in these laboratories have been detailed previously . All solvents were pre‐dried, distilled, and freeze‐pump‐thaw degassed before use .…”

Preparation, Characterization, Electrochemistry, and Infrared Spectro­electrochemistry of Ruthenium ­Nitrosyl Porphyrins Containing η1‐O‐Bonded Axial Carboxylates

“…In all the electrochemical experiments, a three-electrode cell was utilized and consisted of a 3.0-mm diameter Pt disk working electrode, a Pt wire counter electrode, and a Ag/AgCl reference electrode. [12,41,42] Solutions were deaerated before use by passing a stream of N 2 gas through the solution for a minimum of 10 min. A blanket of N 2 was maintained over the solution while performing the experiment; care was taken to minimize evaporative cooling due to N 2 flow in the headspace, as this could cause rolling baselines in the resulting IR difference spectra.…”

“…A Bruker Vector 22 and/or a Tensor 27 FTIR spectrometer equipped with a mid-IR fiber-optic dip probe and liquid nitrogen cooled MCT detector (RemSpec Corporation, Sturbridge, MA, USA) were used for the infrared spectroelectrochemistry. [12,41,42] The electrochemical experiments were performed in triplicate to determine reproducibilities. X-ray diffraction data were collected using a diffractometer with a Bruker APEX ccd area detector and graphite-monochromated Mo-K α radiation (λ = 0.71073 Å).…”

“…[12,41,42] In each of these experiments, the Pt working electrode was held at a potential slightly more positive (for oxidations) than the respective peak potential E pa , or slightly more negative (for reductions) than the respective peak potential E pc . The IR spectra of the neutral compounds in support electrolyte were used as backgrounds for the difference spectra.…”