= Solution
Low-spin Co(III) is substitution-inert. In acid, coordinated ammine <deprotonation> is suppressed, so the strongly donating amido <conjugate base> that assists ligand loss is not generated appreciably. Direct aquation/linkage change consequently remains very slow.
The persistence of the starting S-bound complex therefore supports a \b[base-activated kinetic pathway]. It is consistent with the rapid rearrangement in base and does not <mean> that the S-bound form must be the thermodynamically preferred linkage isomer under every condition.
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