Versatile thin layer spectroelectrochemical cell employing specular reflectance

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The four-coordinate anion Cul(dpym), (Hdpym = 3,3',5,5'-tetramethyl-4.4'-dicarboethoxydipyrromethene) can be prepared in solution in acetone either by electrochemical reduction of the known tetrahedral complex CuH(dpym)? (E' = -290 mV vs. SCE) or by the quantitative reaction of 2Hdpym with Cu(CH,CN),+ in the absence of 0,. The latter reaction does not go to completion in solvents that bind relatively strongly to CU' or that are poor proton acceptors. Ligand exchange between cu'(dpym),-and excess Hdpym in acetone is "fast" in the 'H NMR timeframe, with k, = 1.4 x lo7 L mol-' s-' at 298 K (first order in each reactant), AH^; = 3.4 2 0.6 kJ mol-', and AS,: = -97 ? 3 J K-I mol-'. In the absence of excess Hdpym, dissociation of Cu'(dpym); in acetone remains negligible. Homogeneous electron exchange between Cu1(dpym)< and ~u " ( d~y m )~ in acetone falls in the "slow" 'H NMR timeframe, with kc, = 5.9 x lo3 L mol-' s-I, AH,,$ = 48.5 2 3.0 kJ mol-I, and AS,,* = -10 2 I0 J K-' mol-', at ionic strength I = 0.007 mol L-' and 298 K, while for the same self-exchange on a Pt electrode the heterogeneous rate constant k,, = 0.16 ? 0.04 cm sf' at I = 0.1 mol L-' and 298 K, according to AC voltammetry. These values of kc, and kel are of the order expected for CU"" couples in which no significant change in coordination number or geometry accompanies electron transfer.Key words: Electron transfer, copper complexes, ligand substitution kinetics, dynamic NMR.RCsumCs : On peut prtparer l'anion tktracoordint Cul(dpym),-(Hdpym = 3,3',5,5'-tCtramCthy1-4,4'-dicarboCthoxydipyrromtthene) en solution dans l'acetone soit par une reduction Clectrochimique du complexe tetrakdrique ~u " ( d~~m )~ (EO = -290 mV vs. SCE) ou par la reaction quantitative de 2Hdpym avec le Cu(CH3CN),+ en l'absence de 0,. La dernikre reaction n'est pas complkte dans des solvants qui se lient relativement fortement au CU' ou qui sont de pauvres accepteurs de proton. L'Cchange de coordinat entre le Cul(dpym); et un excks de Hdpym dans l'acetone est rapide par rapport a la RMN du 'H; k, = 1,4 x lo7 L mol-' s-I t i 298 K (premier ordre par rapport B chaque reactif), AH,* = 3. [Traduit par le redaction] couples will tend to be rather slow if the normally preferred According to the Vallee-Williams principle (I), the rates of outer-sphere electron transfer processes involving copper(1ID)

“…The details of the cell design, the rapid scanning spectrometer, and the experimental procedures have been published previously (20,21).…”

Section: Electrochemistry and Spectroelectrochemistrymentioning

confidence: 99%

Electron exchange kinetics in a tetrahedrally coordinated copper(II)/(I) couple

Metelski¹,

Hinman²,

Takagi³

et al. 1995

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“…Analysis of the energy spectra obtained prior to and following electrolysis affords a difference spectrum between oxidized and unoxidized forms of electroactive species within the thin layer cavity. Utilizing this technique, we were able to detect (4,5), in situ, a strong absorbance at 1277 cm-' due to the cation radical of tetraphenylporphinatozinc(I1) (TPPZn) in 1,2-dichloroethane containing tetra-n-butylammonium perchlorate.…”

Section: Introductionmentioning

confidence: 99%

In-situ Fourier transform infrared spectroelectrochemical studies of the oxidation of some tetraphenylporphyrin complexes

Hinman¹,

Pavelich²,

McGarty³

1988

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In-situ FTIR spectroelectrochemistry has been applied to determine difference spectra in the region 1800 to 1000 cm−1 associated with the oxidation of TPPH2, TPPMg, TPPCu, TPPZn, TPPCo, TPPMnCl, and TPPFeCl. In all cases, formation of the π-cation radical results in two characteristic absorbance decreases near 1600 and 1485 cm−1, and five characteristic absorbance increases near 1415, 1350, 1285, 1225, and 1005 cm−1. Formation of the π-dication was observed for TPPZn, TPPMg, and TPPCo, and gave rise to a new absorbance increase near 1600 cm−1, and a shift to higher frequency of bands in the 1200 to 1400 cm−1 region. Perchlorate coordination to oxidized TPPZn, TPPMg, and TPPCo gives rise to bands near 1140 and 1030 cm−1.

“…The optical pathlength was calculated to be 63 p m for this and subsequent experiments, which corresponds to a thin layer thickness of ca. 22 p m (6). During the electrolysis time of 12.0 s, it was possible to collect nine spectra, each obtained by averaging 16 successive scans.…”

Section: Resultsmentioning

confidence: 99%

“…The cell employs a radial concentric configuration of working and counter electrodes, which has previously been shown to be optimum in terms of minimizing the effects of the high solution resistance within the thin layer cavity (2). The advantages of this type of cell and the details of its construction have been fully discussed in a previous publication (6). The only modification in the present work is the inclusion of a thin black card positioned normal to the electrode surface and the plane of incidence of the optical beam, which serves to deflect stray light reflected from the surface of the quartz window.…”

Section: Methodsmentioning

confidence: 99%

Thin-layer ultraviolet–visible reflectance spectroelectrochemistry with a spinning-grating monochromator

Jones¹,

Hinman²

1990

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A thin-layer UV-visible spectroelectrochemistry system has been constructed using a commercially available spinninggrating monochromator. The spectroelectrochemical experiment is capable of scanning a wavelength range of 369 to 617 nm in 2.1 ms. The time delay between successive scans is 83 ms. The maximum peak-to-peak noise level in a 300-point spectrum collected during 2.1 ms with a spectral bandwidth of 2 nm is 0.03 absorbance units. The anodic spectroelectrochemistry of tetraphenylporphinatocopper(II), studied using the system, is presented.