Colorimetric Detection of Cu[II] Cation and Acetate, Benzoate, and Cyanide Anions by Cooperative Receptor Binding in New α,α‘-Bis-substituted Donor−Acceptor Ferrocene Sensors

New ferrocene derivatives bearing two donor−acceptor systems are capable of selectively sensing cations and anions by cooperative binding of the two α,α‘-groups bonded to the ferrocene nucleus, thus permitting the naked-eye selective colorimetric detection of copper[II] cation and acetate, benzoate, or cyanide anions, which are ions of toxicological and biological relevance.