Inner sphere reactions are inhibited by large ligands, which prevent the formation of the crucial bridged intermediate.
Thus, inner sphere ET is rare in biological systems, where redox sites are often shielded by bulky proteins.
Inner sphere ET is usually used to describe reactions involving transition metal complexes and most of this article is written from this perspective.
The discoverer of the inner sphere mechanism was Henry Taube, who was awarded the Nobel Prize in Chemistry in 1983 for his pioneering studies.
When the reaction is carried on in a medium containing radioactive Cl, the mixing of the Cl− attached to Cr(III) with that in solution is less than 0.5%.