outer-sphere reaction

chemistry

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July 1, 2026

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In chemistry, an outer-sphere reaction is a type of oxidation-reduction (redox) process where electron transfer occurs between two chemical species without breaking the bonds within their coordination spheres. This means the ligands, such as water or hydroxide ions, remain attached to the metal ions throughout the reaction.12

This contrasts with inner-sphere reactions, where a bridging ligand connects the two metal ions, facilitating electron transfer through this intermediate. Outer-sphere reactions are often characterized by simple electron or hydrogen atom transfer between intact coordination complexes. The chromium(II)-iron(III) reaction is an example where outer-sphere mechanisms are considered plausible.12

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coordination compound
Oxidation-reduction
…of electron transfer, commonly designated outer-sphere and inner-sphere mechanisms, have been recognized. Outer-sphere electron transfer occurs without dissociation or disruption of the coordination sphere of either complex—i.e., through both intact coordination spheres. The first reaction above is of this type. On the other hand, inner-sphere electron transfer—e.g., the second reaction…
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…of electron transfer, commonly designated outer-sphere and inner-sphere mechanisms, have been recognized. Outer-sphere electron transfer occurs without dissociation or disruption of the coordination sphere of either complex—i.e., through both intact coordination spheres. The first reaction above is of this type. On the other hand, inner-sphere electron transfer—e.g., the second reaction…
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oxidation-reduction reaction
Mechanisms of redox reactions
Outer-sphere reactions are those that take place without breaking any bonds between a metal and a group such as water or hydroxide ion bound to it. Both the simple electron- and hydrogen-atom-transfer mechanisms are outer-sphere processes. If, on the other hand, the oxidation-state changes take…
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Outer-sphere reactions are those that take place without breaking any bonds between a metal and a group such as water or hydroxide ion bound to it. Both the simple electron- and hydrogen-atom-transfer mechanisms are outer-sphere processes. If, on the other hand, the oxidation-state changes take…
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