= Solution
The free end of N-bound $\mathrm{Co{-}NCS}$ is sulfur. Cr(II) binds there, giving the remote bridge $\mathrm{Co^{III}{-}N{-}C{-}S{-}Cr^{II}}$. <Electron transfer> and cleavage of the Co-N bond leave S-bound Cr(III), $\mathrm{[Cr(SCN)(OH_2)_5]^{2+}}$; labile Co(II) becomes hexaaquacobalt(II).
The much smaller <rate constant> shows that the efficiency of bridge formation/<electron> transmission is strongly sensitive to linkage orientation. Efficient donation and coupling in a Co-S-bound precursor need not be reproduced when cobalt is N-bound. Its reduction is still consistent with <inner-sphere electron transfer>; a slow rate alone is not a criterion for outer-sphere transfer.
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