Synthesis, structure and electron-mediator properties of the mono- and difunctionalized macrobicyclic iron(II) tris-dioximates with thiol terminated ribbed spacer substituents

Nucleophilic substitution of the reactive chlorine atoms of mono- and dichlorine clathrochelate FeBd2(HGmCl)(BF)2 and FeBd2(Cl2Gm)(BF)2 precursors (where Bd2−, HGmCl2− and Cl2Gm2− are α-benzyldioxime, chloroglyoxime and dichloroglyoxine dianions, respectively) with HSCH2CH2SH and (HSCH2CH2)2S in the presence of triethylamine afforded the FeBd2(HGmSCH2CH2SH)(BF)2 (1) and FeBd2(HGm(SCH2CH2)2SH)(BF)2 clathrochelates with a sole thiol terminated spacer substituent and the FeBd2((HS(CH2CH2S)2)2Gm)(BF)2 clathrochelate with two longchain thiol-sulfide ribbed groups. The crystal and molecular structures of these complexes were obtained by X-ray crystallography. The clathrochelate molecules possess a geometry intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP). The X-ray data are in a good agreement with the 57Fe Mössbauer parameters for complexes studied. These parameters characterize them as the low-spin iron(II) complexes (the isomeric shift values) with TP–TAP geometry (the quadrupole splitting values). Application of clathrochelate self-assembled monolayer (SAM) as the redox mediators for the determination of hydrogen peroxide is discussed. The calibration curve for hydrogen peroxide concentrations was found to be in the range from 2.0 · 10−6 to 1.6 · 10−5 mol · L−1 with limit of detection equal to 1.0 · 10−6 mol · L−1. The clathrochelate SAM on gold electrode provides precise and sensitive amperometric determination of hydrogen peroxide.