Electrochemical Investigation of Potassium Heptacyanorhenate(III) in Aqueous Solution

Abstract The electrochemistry of potassium heptacyanorhenate(III) in aqueous solution was studied by cyclic and by rotating disk voltammetry at planar microelectrodes. The results are consistent with a single, reversible electron transfer: Re(CN) 3− 7 + e ⇄Re(CN) 4− 7 with E ′ 0 = 643 mV vs. NHE. A single protonation equilibrium is observed: Re(CN) 4− 7 + H + ⇄ Re(CN) 7 H 3− with p K = 1.31 determined from combined voltammetric and pH data. The Re–CN bond appears to be kinetically inert, and none of the cyano complexes in other oxidation states of Re claimed in the literature was found in the potential range − 2 V to + 1 V.