Tunable bis(ferrocenyl) receptors for the solution-phase electrochemical sensing of transition-metal cations

A series of linked bis(ferrocenyl) receptors with a variety of functionality in the spacer linkage was prepared, and their co-ordination properties with metal ions in non-aqueous solution were investigated. In particular, the ability of the ferrocene redox antenna to sense the binding of transition metals was monitored. The type of electrochemical response fell into two classes, dependent on both the metal ion investigated and the nature of the spacer group; the different receptor response mechanisms were assigned to either protonation or metal-ion co-ordination. Co-ordination and protonation therefore compete for this type of receptor in acetonitrile solution, and the affinity of the receptor and observed redox response are directly tunable.