We extended our research on N-benzamidothiourea based anion receptors to N-ferrocamidothioureas and synthesized N-feffocamido-N'-(substituted phenyl)thioureas (3a similar to 3e, substituent X =p-OCH3, p-CH3, H, m-Br, and m-CF3). In 3a similar to 3e an electrochemically active ferrocene moiety was employed as an aromatic counterpart of phenyl and -NH- was a spacer linking ferrocene signal reporter and the thiourea binding-site. Cyclic voltammetric experiments carried out in acetonitrile indicated that the half-wave potentials of 3a similar to 3e of 0.31 V vs. Ag/AgNO3 were independent of the substituent at N'-phenyl ring. It was found that the H-1 NMR chemical shifts of the aromatic protons at ferrocene moiety and the amido -NH proton in 3 did not, whereas those of the M-phenyl aromatic protons and the thioureido -NH protons did vary when the N'-phenyl substituent was changed. The azino N-N bond was hence concluded to be twisted that blocked the electronic communication between the ferrocene moiety and thiourea anion-binding site. Yet we experimentally observed that the oxidation potentials of 3a similar to 3e shifted by ca. -200 mV in the presence of anions such as CH3CO2- and F- in acetonitrile and the chemical shifts of the ferrocene aromatic protons shifted to high field upon anion binding to the thiourea moiety in 3a similar to 3e. A conformation change in the N-N bond was hence assumed for 3a similar to 3e upon anion binding. Absorption titrations indicated that anion binding to 3a similar to 3e resulted in-a new absorption band at ca. 315 nm with a spectral red-shift of 5820 cm(-1) irrespective of the substituent. The spectral red-shift, anion affinity of 10(6) mol(-1).L orders of magnitude for CH3CO2- and F-, and substituent effect on the anion affinity of 3a similar to 3e were found much higher than those of the corresponding traditional N,N'-diphenylthiourea counterparts (1). It was concluded that anion binding induced conformational change in 3a similar to 3e led to enhanced anion affinity and substituent effect on the anion affinity, information indicative of allosteric character of the receptors and instructive for designing N-arylamido-N'-arylthiourea based anion receptors. Results reported here further supported the advantages of the" NH-" spacer in N-benzamidothiourea-based anion receptors
