Sun Dong, Hughbanks Timothy
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012.
Inorg Chem. 1999 Mar 8;38(5):992-997. doi: 10.1021/ic981182p.
Ambient temperature AlCl(3)-1-ethyl-3-methylimidazolium chloride (ImCl) molten salts, both basic (40/60 mol % AlCl(3)/ImCl) and acidic (60/40 mol % AlCl(3)/ImCl), were used in an electrochemical investigation of centered hexanuclear zirconium halide clusters. In the basic molten salt, these (Zr(6)ZCl(12))Cl(6) (Z = Be, B, C, Mn, Fe) centered clusters exhibit the following electrochemical reactions on a glassy carbon electrode (potentials vs Al/Al(3+)): (Zr(6)BeCl(12))Cl(6)()(-) + e(-) right harpoon over left harpoon (Zr(6)BeCl(12))Cl(6)(-), E(1/2) = -0.613 V (n = 4), E(1/2) = -1.085 V (n = 5); (Zr(6)BCl(12))Cl(6)()(-) + e(-) right harpoon over left harpoon (Zr(6)BCl(12))Cl(6)(-), E(1/2) = -0.365 V (n = 4), E(1/2) = 0.072 V (n = 3); (Zr(6)CCl(12))Cl(6)()(-) + e(-) right harpoon over left harpoon (Zr(6)CCl(12))Cl(6)(-), E(1/2) = 0.230 V (n = 3); (Zr(6)MnCl(12))Cl(6)(-) + e(-) right harpoon over left harpoon (Zr(6)MnCl(12))Cl(6)(-), E(1/2) = -0.432 V. In the acidic melt, only electrochemical reactions (Zr(6)BeCl(12))(AlCl(4))(6)()(-) + e(-) right harpoon over left harpoon (Zr(6)BeCl(12))(AlCl(4))(6)(-), E(1/2) = -0.069 V (n = 5), E(1/2) = 0.504 V (n = 4), and (Zr(6)BCl(12))(AlCl(4))(6)(-) + e(-) right harpoon over left harpoon (Zr(6)BCl(12))(AlCl(4))(6)(-), E(1/2) = 0.700 V are clearly observed. These data is consistent with less systematic observations of oxidation of these clusters in solution. No unambiguous one-electron electrochemical reduction nor oxidation is observable for the Fe-centered cluster in the ionic liquids. The half-wave potentials of the above reactions of the Be-, B-, C-, and Mn-centered clusters are controlled largely by clusters' charges. This correlation of redox potentials allows a useful direct comparison with data for related hexanuclear niobium clusters in the literature.
