Highly branched ferrocene-functionalised polyazacycloalkanes as electroactive receptors for transition-metal ions

Reaction of N,N',N '',N'''-tetrakis (2-aminoethyl)-1,4,8,11-tetraazacyclotetradecane (taec) with ferrocenecarbaldehyde and further reduction with LiAlH4 resulted in the synthesis of the redox-active receptor N,N',N '',N'''-tetrakis(4-ferrocenyl-3-azabutyl)-1,4,8,11-tetraazacyclotetradecane (tfabc); The protonation behaviour of tfabc and its complex formation with Cu-II, Zn-II and Cd-II have been studied in tetrahydrofuran-water (70:30 v/v) (0.1 mol dm(-3) NBu(4)(t)ClO(4), 25 degrees C). The potentiometric and electrochemical data indicate the formation of 1:1 and 1:2 (tfabc:M(2+)) stoichiometries. The E(1/2) values for tfabc shift as a function of the pH from 389 (pH 10) to 482 mV (pH 2.5) and E(1/2) vs. pH curves for the tfabc-H+-M(2+) systems (M = Cu, Zn or Cd) show that tfabc electrochemically recognises the presence of copper(II) selectively at pH < 5. The shift of E(1/2) appears to be caused by electrostatic forces and the E(1/2) vs. pH curves can be predicted in terms of the distribution diagrams of the tfabc-H+-M(2+) systems.