Carboxy-bound chromium(IV); a formal potential and estimated self-exchange rate for CrIII,IV pertaining to 2-ethyl-2-hydroxybutanoate chelates

Abstract

Pink solutions containing a stabilized complex of Cr^IV result from reduction of HCrO₄^– with H₃AsO₃ in media buffered by 2-ethyl-2-hydroxybutanoic acid (Hehb); redox reactions of this atypical state lead to a calculated E° of 0.96 ± 0.02 V for Cr^III,IV and an estimated self-exchange rate 10^{–2.6 ± 0.6} dm³ mol^–1 s^–1(25 °C, µ= 0.5 mol dm^–3), the latter value supporting a six-coordinate structure of Cr^IV(ehb)₂, rather than a five-coordinate Cr^IV(O) species.