Synthesis, spectroscopy and electrochemistry of some polynuclear complexes of aminoethanethiol

Polynuclear S-bridged complexes of the general formula {Co₂L₆]M}ⁿ⁺ with M = Co(III), Cd(II), Pb(II), Ni(II), Zn(II) and Hg(II) were prepared from Co(2-aminoethanethiolate)₃] and the appropriate metal salt. Proton and ¹³C NMR spectra are consistent with structures previously proposed for these species with ¹³C chemical shifts dependent on the bridging metal ion. Electrochemical studies are consistent with a model in which an S-bonded ML₆ moiety (i.e., the bridging metal ion and the six aminoethanethiolate ligands) acts as a ‘dodecadentate’ ligand bonded to two Co³⁺ ions. Reduction of the terminal cobalt ions in these trinuclear complexes is observed in the range ?0.75 to ?1 V vs. SCE on mercury, gold or glassy carbon working electrodes. For complexes with relatively labile bridging ions, the electrode reaction is irreversible, presumably due to rapid decomposition of the labile cobalt(II) product. For the tricobalt(III) derivative, however, the electrode reaction is reversible consistent with other recent observations on cage or otherwise stereorestrictive ligand systems 1].