Abstract
The new ligand, [Fc(cyclen)~2~] (5) (Fc=ferrocene, cyclen=1,4,7,10‐tetraazacyclododecane), and corresponding Zn^II^ complex receptor, Fc{Zn(cyclen)(CH~3~OH)}~2~~4~ (1), consisting of a ferrocene moiety bearing one Zn^II^‐cyclen complex on each cyclopentadienyl ring, have been designed and prepared through a multi‐step synthesis. Significant shifts in the ^1^H NMR signals of the ferrocenyl group, cf. ferrocene and a previously reported [Fc{Zn(cyclen)}]^2+^ derivative, indicated that the two Zn^II^‐cyclen units in 1 significantly affect the electronic properties of the cyclopentadienyl rings. The X‐ray crystal structure shows that the two positively charged Zn^II^‐cyclen complexes are arranged in a trans like configuration, with respect to the ferrocene bridging unit, presumably to minimise electrostatic repulsion. Both 5 and 1 can be oxidized in 1:4 CH~2~Cl~2~/CH~3~CN and Tris‐HCl aqueous buffer solution under conditions of cyclic voltammetry to give a well defined ferrocene‐centred (Fc^0/+^) process. Importantly, 1 is a highly selective electrochemical sensor of thymidilyl(3′‐5′)thymidine (TpT) relative to other nucleobases and nucleotides in Tris‐HCl buffer solution (pH 7.4). The electrochemical selectivity, detected as a shift in reversible potential of the Fc^0/+^ component, is postulated to result from a change in the configuration of bis(Zn^II^‐cyclen) units from a trans to a cis state. This is caused by the strong 1:1 binding of the two deprotonated thymine groups in TpT to different Zn^II^ centres of receptor 1. UV‐visible spectrophotometric titrations confirmed the 1:1 stoichiometry for the 1:TpT adduct and allowed the determination of the apparent formation constant of 0.89±0.10×10^6^ M^−1^ at pH 7.4.