The guanidine unit in the guise of 2-aminoimidazole in the new structural motif 2-arylamino-1,3-diaza[3]ferrocenophane 4 acts as a binding site for anions. The electrochemical behavior of this compound has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) and was found to exhibit a quasi reversible oxidation peak, associated to the Fe(II)/Fe(III) redox couple (Ep = 440 mV), and a non-reversible oxidation wave (Ep = 817 mV), probably associated to the oxidation of the C=N unit present in the guanidine bridge. Recognition of AcO-, PhCO2-, F-, Cl-, and Br- anions by the free receptor and the less basic anions Br-, Cl-, and NO3- by its monoprotonated form takes place by unusual redox-ratiometric measurements and spectroscopic (H-1 NMR and UV-vis) changes.