Here’s the difference:
Inner-sphere electron transfer
- The two reacting complexes are connected directly by a bridge ligand (a ligand that links both metals).
- The electron moves through this bridge.
- Bonds are often temporarily rearranged during the process.
Outer-sphere electron transfer
- The two reacting complexes do not share ligands.
- They stay separate, and the electron “jumps” from one metal center to the other through space or solvent.
- The original bonds around each complex usually stay unchanged.
In short:
- Inner sphere = electron transfer through a shared ligand bridge.
- Outer sphere = electron transfer without direct bonding, just from one complex to another.