Electrochemistry and surface-enhanced Raman spectroscopy (SERS) of adsorbed chromium–bipyridyl complexes†

Abstract

= polyacrylic acid) were studied at silver and glassy carbon electrodes by cyclic voltammetry. On reduction, slow electron transfer reactions giving adsorbed species are evident from the cyclic voltammograms. In situ surface-enhanced Raman spectroscopy (SERS) of the aquahydroxo and dimer complexes shows a broad, intense Cr-O vibration at around 550 cm 21 . This arises as the exciting line (514.5 nm) is close to resonance with the lowest energy absorption band assigned to a ligand field transition ( 4 A 2g ? 4 T 2g ). At 20.4 V SERS spectra show features of both the normal Raman spectrum of [Cr(bpy) 3 ] 3+ and the colloidal SERS of [Cr(bpy) 3 ] 2+ and can be explained by the presence of partially-reduced adsorbed species. The electron is localized first on to the metal and then on to one of the bpy ligands as follows: [Cr III (bpy 0 ) 2 X 2 ] n+ + e ?[Cr II (bpy 0 ) 2 X 2 ] (n21)+ and [Cr II (bpy 0 ) 2 X 2 ] (n21)+ + e ?[Cr II (bpy 2 )(bpy 0 ) 2 X 2 ] (n22)+ . Although the SERS evidence suggested that the integrity of the complexes is maintained during the reaction, prolonged electrolysis leads to hydrolysis and/or substitution of the complexes. Thus [(PVP) 2 -Cr(bpy) 2 ] 3+ can be electrosynthesized by reduction of cis-[Cr(bpy)Cl 2 ] + at a PVP modified glassy carbon electrode and shows a characteristic peak at 20.32 V.

Unusual Behavior of a Novel Heterogeneous Chiral Dimer Cr(III)−Salen Complex in the Epoxidation/Epoxide Ring-Opening Reaction of trans-Methylcinnamate Ester

“…vibration at around 550 cm −1 , a band located at around 310 cm −1 , which can be attributed to Cr−N str. vibration in agreement with ref , and two intense bands located at 1350−1400 cm −1 atributted to C−C vibration.…”

Surface-enhanced resonance Raman spectroscopy of Ru and Os polyvinylpyridine adsorbed on silver electrodes

“…The observed damping factor for the SERS signal is such that the intensity appears to decay faster with coverage than predicted by eqn. (10). That is, the SERRS intensity seems to drop faster with coverage than the RR increases in Fig.…”

“…12 Theoretical curves based on eqn. (10) for the absorption corrected SERRS intensity nm) vs. loading. The attenuation (j inc \ 514.5 factor 0.055C was used rather than the assumed 0.042C value.…”

“…9 Although many di †erent electrochemical and spectroscopic methods have been applied to the study of CMEs SER spectroscopy has proved to be one of the most informative in situ techniques. 10 The theoretical basis of SERS was a matter of controversy for many years but a consensus has now emerged, as reÑected in several recent reviews.11h15 It is clear that the overall enhancement of Raman signal, which may be as large as 106, has two distinct contributions : Ðrst, laser irradiation may result in the excitation of plasmons within the metal surface, producing a classical electromagnetic enhancement (EM mechanism) and, secondly, chemisorption may result in the creation of new adsorbate energy levels (chemical or CT mechanism). The EM mechanism is generally expected to produce the major contribution to the enhancement, explaining why (a) SERS is limited to a small range of metals for which surface plasmons may be excited by visible radiation, e.g.…”

Dissociation kinetics at polyacrylic latex-coated electrodes

“…Poly(acrylic acid) (PAA) has been used electrochemically for uptake of redox cations, e.g., bis-bipyridyl cobalt [1,2], cadmium in the presence of alumina [3], cupper [4], tris(2,2 0 -bipyridyl)ruthenium [5], nickel(II) tetraazamacrocyclic complex [6], bis-bipyridyl osmium [7], hexaammineruthenium and hexaamminecobalt [8], ferrocenylethanol [9], thallium [10], some alkali metal hydroxides without salts [11], and N,N-dimethylaminomethyl-ferrocene [12]. Negatively charged molecules such as hexacyanoferrate cannot be simply taken up to PAA [5].…”