Electron spin resonance and electrochemical study of thiohydroxamate and 1-phenyl-3-imino-2(1H)-pyridinethione complexes of copper(II)

Article abstract of DOI:10.1021/ic00135a020

Syntheses, electronic spectra, ESR spectra, and electrochemical properties are described for a range of {S,O} chelates of copper(II)-containing bidentate thiohydroxamic acids, viz., Cu(RC(=S)N(R′)O)₂, and for two tetredentate {S,N} 1-phenyl-3-imino-2(1H)-pyridinethione complexes. Both classes of compounds have square-planar geometries; the thiohydroxamates have a trans-{S₂,O₂} chromophore while the pyridinethione derivatives have a cis-{S₂,N₂} chromophore. S → Cu(II) charge-transfer bands are observed in the UV-visible spectra. Unusual solvent-dependent changes in the visible spectra are displayed by the R′ = H thiohydroxamates. The ESR spectra of the thiohydroxamate complexes give well-resolved lines with narrow line widths. Some unusual splittings of the parallel lines in the frozen solution spectra and in the four-line fluid solution spectra are observed. The ESR spectra of the Cu{S₂,N₂} complex show broader and less well-resolved line shapes. Polographic and cyclic voltammetric measurements on DMF solutions of the compounds are discussed in detail. The Cu(II)/Cu(I) reduction potentials are compared with those of related thio complexes and with those of copper redox proteins. A brief discussion of the likely binding groups in the active sites of copper proteins is given.