Electrochemistry of transition metal halide and oxide halide complexes in room temperature haloaluminate ionic liquids

The electrochemistry and absorption spectroscopy of the anionic iridium, niobium, and osmium chloride complexes and the niobium oxide chloride complexes were investigated in the basic composition region of the room temperature haloaluminate ionic liquid, aluminum chloride-1-methyl-3-ethylimidazolium chloride (AlCl{dollar}sb3{dollar}-MeEtimCl). The bromide complexes of iron and titanium were subjected to similar studies in the related aluminum bromide-1-methyl-3-ethylimidazolium bromide (AlBr{dollar}sb3{dollar}-MeEtimBr) system. In addition, a procedure for removing oxide impurities from the AlCl{dollar}sb3{dollar}-MeEtimCl molten salt with phosgene was explored.; Both the (IrCl{dollar}sb6{dollar}) {dollar}sp{lcub}2-/3-{rcub}{dollar} and the (OsCl{dollar}sb6{dollar}) {dollar}sp{lcub}2-/3-{rcub}{dollar} redox systems exhibit classical reversible, uncomplicated electrochemical behavior at glassy carbon electrodes in the basic AlCl{dollar}sb3{dollar}-MeEtimCl ionic liquid in contrast to their behavior in aqueous solution. Electronic absorption spectra that were recorded for the (IrCl{dollar}sb6{dollar}) {dollar}sp{lcub}2-{rcub}{dollar}, (IrCl{dollar}sb6{dollar}) {dollar}sp{lcub}3-{rcub}{dollar}, (OsCl{dollar}sb6{dollar}) {dollar}sp{lcub}2-{rcub}{dollar}, and (OsCl{dollar}sb6{dollar}) {dollar}sp{lcub}3-{rcub}{dollar} complexes in this solvent show no evidence of the distortions due to solvation and solvolysis phenomena that are commonly seen in the spectra of these ions in many molecular solvents.; Electronic absorption spectroscopy indicated that niobium(V) is complexed as (NbCl{dollar}sb6{dollar}) {dollar}sp-{dollar} in basic AlCl{dollar}sb3{dollar}-MeEtimCl. This species can be reduced to (NbCl{dollar}sb6{dollar}) {dollar}sp{lcub}2-{rcub}{dollar} and (NbCl{dollar}sb6{dollar}) {dollar}sp{lcub}3-{rcub}{dollar} in two successive, one-electron, reversible electrode reactions. It is possible to prepare stable solutions of the latter species by using controlled potential electrolysis. The addition of oxide in the form of Li{dollar}sb2{dollar}CO{dollar}sb3{dollar} to solutions of (NbCl{dollar}sb6{dollar}) {dollar}sp-{dollar} produces (NbOCl{dollar}sb5{dollar}) {dollar}sp{lcub}2-{rcub}{dollar}, which can be electrochemically reduced to a magenta colored niobium(IV) complex, possibly (NbOCl{dollar}sb4{dollar}) {dollar}sp{lcub}2-{rcub}{dollar}. The Nb(V)/Nb(IV) oxide chloride electrode reaction exhibits quasireversible behavior.; Iron(III) and titanium(IV) appear to be complexed as (FeBr{dollar}sb4{dollar}) {dollar}sp-{dollar} and (TiBr{dollar}sb6{dollar}) {dollar}sp{lcub}2-{rcub}{dollar}, respectively, in basic AlBr{dollar}sb3{dollar}-MeEtimBr. Both species undergo one-electron, reversible electrode reactions in this solvent similar to those observed for their chloride analogs in AlCl{dollar}sb3{dollar}-MeEtimCl.; Stokes-Einstein products were estimated for each of the complexes examined in this study. The relative radii of the diffusing species, which were estimated from these products, were found to be strongly dependent upon the overall charge of each complex ion and were relatively independent of the oxidation state of the metal core or the coordination geometry of the complex. (Abstract shortened with permission of author.)...