Strong bridging ligands

Further data on this reaction are summarised in Table 20. The role of complexing anions is clear from the kinetics and also from relative rates. It appears that strongly bound ligands are associated with second-order reduction but that weakly bound ligands such as H2O result in a third-order reaction. One view of the third-order term for dilute sulphuric acid (as for aqueous HCIO4) is that the active reductant is a bridged species of the type (Fe S04 Fe ) . 

The Type 1 copper ions are normally coordinated by three strong ligands, a cysteine and two histidines, and often have one or two weaker ligands such as methionine sulfur or oxygen. Type 3 coppers are usually each coordinated by three histidines, with a bridging ligand such as oxygen or hydroxyl anion. 

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