Complexation and electrochemical sensing of anions by amide-substituted ferrocenyl ligands

New amide-containing ferrocenyl ligands, L1–5, were prepared and the voltammetric and 1H NMR investigations of anion binding were carried out in organic media. The electrochemical recognition ability of L1–5 towards F−, HSO4−, H2PO4− and ATP2− is based on the synergy between H-bonding to amide protons in anion complexation to reduced, neutral ligands and ion-pairing interactions developed with the oxidized, cationic form of the ligands. The strength of the anion–ligand interactions depends on the number of ferrocene centers and amide groups in the receptor, and on the accessibility of the binding sites. Clear two-wave cyclic voltammetry features allowed the amperometric titration of H2PO4− and ATP2− by ligands L4 and L5 built from a cyclotriveratrylene structural unit, and containing a combination of three ferrocene centers with three (L4) or six (L5) amide groups.