Electron transfer reactions between penta-ammine(nitrilotriacetato)-cobalt(III) and chromium(II) and between acetatopenta-amminecobalt(III) and N-methyliminodiacetato-chromium(II)

Abstract

The complex [Co(NH3)5(H2nta)]2+(nta3–= nitrilotriacetate) reacts with CrII with the rate law –d[CoIII]/dt=k′[Co(NH3)5(H2nta)2+][Cr2+]aH–2 with k′= 2.45 mol dm–3 s–1 at 25 °C and ionic strength 1.0 mol dm–3(Na[ClO4]). A binuclear intermediate [Co(NH3)5(nta)Cr]2+ is proposed and the specific rate of internal electron transfer is estimated to be ca. 600 s–1. The rate of reaction of [Co(NH3)5(O2CMe)]2+ with CrII is enhanced by the presence of N-methyliminodiacetic acid (H2mida). The rate law is –d[CoIII]/dt=k2′[Co(NH3)5(O2CMe)2+]-[Cr2+][HL–]aH–1 with k2′= 0.24 dm3 mol–1 s–1 at 25 °C, and ionic strength 1.0 mol dm–3(Na[ClO4]). The specific rate for the bimolecular reaction [Co(NH3)5(O2CMe)]2++[Cr(mida)] is estimated to be 18 dm3 mol–1 s–1. The results are discussed in relation to the analogous reactions involving FeII as reductant.