Bidimensional spectroelectrochemistry: application of a new device in the study of a o-vanillin-copper(II) complex

A new bidimensional spectroelectrochemistry setup for UV-Vis absorption measurements has been developed. The new device has been used to follow electrochemical reactions using two different arrangements: 1) a near-normal configuration that supplies information about the processes taking place both on the electrode surface and in the solution adjacent to it, and 2) a long-optical-pathway configuration based on a mobile slit that controls the position of a light beam passing parallel and adjacent to the electrode surface providing information only about the processes taking place in solution during the electrochemical reaction. The new setup has been validated using o-tolidine, a typical reference system for spectroelectrochemistry. The electrochemical mechanism of oxidation/reduction of Cu(o-Va)2(H2O)2 complex (o-Va = o-Vanillin = 2-hydroxy-3-methoxybenzaldehyde) has been studied using bidimensional UV-Vis absorption spectroelectrochemistry. This Cu(II) complex exhibits antimutagenic, anticarcinogenic and superoxide dismutase mimic properties.Junta de Castilla y León (BU033U16), and Ministerio de Economía y Competitividad (CTQ2014-55583-R, CTQ2014-61914-EXP, CTQ2015-71955-REDT)CONICET, UNLP, Junta de Castilla y León (BU033U16), and Ministerio de Economía y Competitividad (CTQ2014-55583-R, CTQ2014-61914-EXP, CTQ2015-71955-REDT

Electron transfer reactions of organometallic compounds

The mixed valence states of the twelve ligand bridged hexaruthenium clusters \rm Ru\sb3(\mu\sb3-O)($\mu$-\rm CH\sb3CO\sb2)\sb6(CO)(L\sp\prime)(\mu-L)\rm Ru\sb3(\mu\sb3-O)($\mu$-\rm CH\sb3CO\sb2)\sb6(CO)(L\sp{\prime\prime}) (L = 1,4-pyrazine or 4,4\sp\prime-bipyridine; L\sp\prime (or L\sp{\prime\prime}) = 4-dimethyl-aminopyridine, pyridine, 4-cyanopyridine, undergo rapid intramolecular electron transfer. The splitting of the reduction waves in cyclic voltammetry depends on the electronic coupling H\rm\sb{AB} between the triruthenium centers, and varies from $\u3c$50 mV to 440 mV. The mixed valence states also exhibit intervalence charge transfer (ICT) bands which provide estimates of H\rm\sb{AB} in the range 6050 cm\sp{-1} to 1310 cm\sp{-1}. The magnitude of the electronic coupling H\rm\sb{AB} strongly influences the IR spectra of the mixed valence states in the $\nu$(CO) region. In the case of relatively weak electronic coupling two $\nu$(CO) bands are clearly resolved. In the case of strong electronic coupling these bands broaden to a single $\nu$(CO) absorption band. These data allow the rate constants, k\rm\sb{e}, for electron transfer in the mixed valence states of pyrazine bridged compounds to be estimated by simulating dynamical effects (with Bloch equations) on $\nu$(CO) absorption band shape at \rm9\times10\sp{11}\ s\sp{-1} (L\sp\prime = 4-dimethyl-aminopyridine) and \rm5\times10\sp{11}\ s\sp{-1} (L\sp\prime = 4-pyridine). The less strongly coupled 4,4\sp\prime-bipyridine bridged complexes also undergo intramolecular electron transfer slower than the IR vibrational time scale. Asymmetric compounds with different pyridine ligands on two sides show asymmetric spectra. The IR intensity between the peaks for neutral and doubly reduced states correlates well with the rate of electron transfer. The spectra of compounds in which CO was substituted by an isocyanide ligand as well as compounds with L = p-phenylene diisocyanide bridge were shown to exhibit Fermi resonance. The superreducing ability of photogenerated 19e- radicals of the type W(CO)\rm\sb5(THF)\sp{\cdot-} was shown to be attenuated by large reorganizational energies associated with the electron transfer step