Electrochemistry of centered hexanuclear zirconium halide clusters in ambient-temperature chloroaluminate molten salts

摘要

Ambient temperature AlCl3-1-ethyl-3-methylimidazolium chloride (ImCl) molten salts, both basic (40/60 mol % AlCl3/ImCl) and acidic (60/40 mol % AlCl3/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](n-) (Z = Be, B, C, Mn, Fe) centered clusters exhibit the following electrochemical reactions on a glassy carbon electrode (potentials vs Al/Al3+): [(Zr6BeCl12)Cl-6](n-) + e(-) reversible arrow [(Zr6BeCl12)Cl-6]((n+1)-), E-1/2 = -0.613 V (n = 4), E-1/2 = -1.085 V (n = 5); [(Zr6BCl12)Cl-6](n-) + e(-) reversible arrow [(Zr6BCl12)Cl-6]((n+1)-), E-1/2 = -0.365 V (n = 4), E-1/2 = 0.072 V (n = 3); [(Zr6CCl12)Cl-6](n-) + e(-) reversible arrow [(Zr6CCl12)Cl-6]((n+1)-), E-1/2 = 0.230 V (n = 3); [(Zr6MnCl12)Cl-6](4-) + e(-) reversible arrow [(Zr6MnCl12)Cl-6](5-), E-1/2 = -0.432 V. In the acidic melt, only electrochemical reactions [(Zr6BeCl12)(AlCl4)(6)](n-) + e(-) reversible arrow [(Zr6BeCl12)(AlCl4)(6)]((n+1)-), E-1/2 = -0.069 V (n = 5), E-1/2 = 0.504 V (n = 4), and [(Zr6BCl12)(AlCl4)(6)](4-) + e(-) reversible arrow [(Zr6BCl12)(AlCl4)(6)](5-), 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. [References: 32]