The discoverer of the inner sphere mechanism was Henry Taube, who was awarded the Nobel Prize in Chemistry in 1983 for his pioneering studies.  A particularly historic finding is summarized in the abstract of the seminal publication.
)Cl is reduced by Cr in M [meaning 1 M]  HClO, 1 Cl appears attached to Cr for each Cr(III) which is formed or Co(III) reduced.  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%.  This experiment shows that transfer of Cl to the reducing agent from the oxidizing agent is direct…"</blockquote>
The paper and the excerpt above can be described with the following equation:
:[CoCl(NH)]  +  [Cr(HO)] →  [Co(NH)(HO)]  +  [CrCl(HO)]
The point of interest is that the chloride that was originally bonded to the cobalt, the oxidant, becomes bonded to chromium, which in its +3 oxidation state, forms kinetically inert bonds to its ligands.  This observation implies the intermediacy of the bimetallic complex [Co(NH)(μ-Cl)Cr(HO)], wherein "μ-Cl" indicates that the chloride bridges between the Cr and Co atoms, serving as a ligand for both.  This chloride serves as a conduit for electron flow from Cr(II) to Co(III), forming Cr(III) and Co(II).