Redox equilibration observed for the reduction of a ruthenium(III) complex by ascorbate under low driving force conditions

A detailed kinetic study of the reduction of trans-[RuCl2(dipicOEt)2]–, where dipic OEt = dipicolinate monoethyl ester anion, by L-ascorbic acid that leads to the formation of the corresponding RuIIcomplex, was carried out spectrophotometrically using the stopped-flow technique. The reaction was studied as a function of [AscH2]Tand pH. The observed kinetic traces could only be fitted by a three-exponential function, characteristic of three parallel reaction paths. The complex was isolated as {[Na(H2O)2][trans-RuCl2(dipicOEt)2]}n, of which a single-crystal X-ray diffraction structure was determined. Detailed spectroscopic studies on the complex in aqueous solution showed that, under the selected experimental conditions, only a single complex species is present in solution. The observed complication is suggested to arise from the low driving force of the reaction during which the reoxidation of RuIIby the semi-oxidized-ascorbic acid, that is, ascorbyl radical Asc·–, accounts for the apparent three-exponential behavior of the reaction.The results are in excellent agreement with those of a recent study on the same reaction forcis-dichloridobispicolinato-ruthenate(III

Reactivity difference between protolytic forms of some macrocyclic chromium(III) complexes in ligand substitution and electron transfer processes

The review provides insight into the mechanism of ligand substitution and electron transfer (from chromium( III) to iron(III)) by comparison of the reactivity of some tetraazamacrocyclic chromium(III) complexes in the conjugate acid-base forms. Use of two geometrical isomers made possible to estimate the influence of geometry and protolytic reactions in trans and cis position towards the leaving group on the rate enhancement. Studies on the reaction rates in different media demonstrated the role played by outer sphere interactions in a monodentate ligand substitution

Inorganic reaction mechanisms. A personal journey

This review covers highlights of the work performed in the van Eldik group on inorganic reaction mechanisms over the past two decades in the form of a personal journey. Topics that are covered include, from NO to HNO chemistry, peroxide activation in model porphyrin and enzymatic systems, the wonder-world of RuIII(edta) chemistry, redox chemistry of Ru(iii) complexes, Ru(ii) polypyridyl complexes and their application, relevant physicochemical properties and reaction mechanisms in ionic liquids, and mechanistic insight from computational chemistry. In each of these sections, typical examples of mechanistic studies are presented in reference to related work reported in the literature

Structure and reactivity of [RuII(terpy)(N^N)Cl]Cl complexes: consequences for biological applications

The crystal structures of [RuII(terpy)(bipy)Cl]Cl·2H2O and [RuII(terpy)(en)Cl]Cl·3H2O, where terpy = 2,2′:6′,2′′-terpyridine, bipy = 2,2′-bipyridine and en = ethylenediamine, were determined and compared to the structure of the complexes in solution obtained by multi-nuclear NMR spectroscopy in DMSOd-6 as a solvent. In aqueous solution, both chlorido complexes aquate fully to the corresponding aqua complexes, viz. [RuII(terpy)(bipy)(H2O)]2+ and [RuII(terpy)(en)(H2O)]2+, within ca. 2 h and ca. 2 min at 37 °C, respectively. The spontaneous aquation reactions can only be suppressed by chloride concentrations as high as 2 to 4 M, i.e. concentrations much higher than that found in human blood. The corresponding aqua complexes are characterized by pKa values of ca. 10 and 11, respectively, which suggest a more labile coordinated water molecule in the case of the [RuII(terpy)(en)(H2O)]2+ complex. Substitution reactions of the aqua complexes with chloride, cyanide and thiourea show that the [RuII(terpy)(en)(H2O)]2+ complex is 30-60 times more labile than the [RuII(terpy)(bipy)(H2O)]2+ complex at 25 °C. Water exchange reactions for both complexes were studied by 17O-NMR and DFT calculations (B3LYP(CPCM)/def2tzvp//B3LYP/def2svp and ωB97XD(CPCM)/def2tzvp//B3LYP/def2svp). Thermal and pressure activation parameters for the water exchange and ligand substitution reactions support the operation of an associative interchange (Ia) process. The difference in reactivity between these complexes can be accounted for in terms of π-back bonding effects of the terpy and bipy ligands and steric hindrance on the bipy complex. Consequences for eventual biological application of the chlorido complexes are discussed

Evaluation of multi-layered graphene nano-platelet composite coatings for corrosion control part I - contact potentials and gas permeability

The electronic and diffusion-blocking properties of graphene nano-platelets (GNPs) are quantified with a view to understanding their action as (possible) additives to anti-corrosion coatings. Platelet size and thickness are determined by SEM and BET specific surface area measurements. A Scanning Kelvin probe is used to show that a contact potential of up to 1.4 V develops between GNP particles and various metal substrates: silver, copper, iron and zinc. A novel photochemical method is used to show that oxygen permeation rates through a PVB-GNP (polyvinylbutyral) composite coating decrease by over an order of magnitude as GNP volume fraction increases to 0.056