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 CrIV 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 CrIII,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 CrIV(ehb)2, rather than a five-coordinate CrIV(O) species.