Steric Crowding in Coordination Compounds: Electron‐transfer kinetics of the [Co(tmen) 3 ] 3+/2+ couple (tmen = 2,3‐dimethylbutane‐2,3‐diamine)

The [Co(tmen) 3 ] 3+ complex ion (tmen = 2,3‐dimethylbutane‐2,3‐diamine) has been synthesized and its redox characteristics compared to those of its parent ion [Co(en) 3 ] 3+ . The 12 peripheral Me groups significantly affect the properties of the [Co(tmen) 3 ] 3+ ion. The ligand‐field bands are shifted to lower energies by about 1700 cm −1 compared to [Co(en) 3 ] 3+ . The reduction potential for [Co(tmen) 3 ] 3+ is +0.28 V ( vs. NHE) compared to −0.18 V for [Co(en) 3 ] 3+ . The rate of the self‐exchange reaction for the [Co(tmen) 3 ] 3+/2+ couple, k = 8.5 × 10 −8 M −1 ·S −1 was determined by applying the Marcus cross‐relation with the reductants Cr 2+ , V 2+ , Eu 2+ , Ru 2+ , and [Co(sepulchrate)] 2+ .