PAPER: Electron transfer reactions of self- assembled monolayers of thio(phenylacetylene)n-substituted chiral metal-salen complexes

Nielsen, M.; Larsen, N. B.; Gothelf, K. V.

Langmuir 2002, 18, 2795–2799, doi: 10.1021/la015715+

Center for Metal-Catalyzed Reactions, Department of Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark

The Danish Polymer Centre, Risø National Laboratory, P.O. Box 49, DK-4000 Roskilde, Denmark

Abstract

This paper describes immobilization of salen ligands in self-assembled monolayers (SAMs) on gold surfaces. The two salen ligands were attached to the gold surface via thio(phenylacetylene)n (n = 1, 2) substituents. The resulting SAMs have been analyzed using ellipsometry and X-ray photoelectron spectroscopy. These measurements showed that high-density monolayers formed on the gold surface (0.20 and 0.30 nmol/cm2 for n = 1 and 2, respectively). MnIIICl, CoIIICl, and FeIIICl were incorporated in the core of the salen ligands immobilized on a gold electrode. The electron-transfer reactions of these metal−salen monolayers were studied by cyclic voltammetry in tetrahydrofuran, and reversible redox reactions between MIII and MII (M = Mn, Co, and Fe) were observed under anaerobic conditions. In the presence of oxygen, the Mn−salen complex underwent an irreversible two-electron reduction. The coverage of the electroactive metal−salen complexes varied from 0.04 to 0.18 nmol/cm2 depending on the metal. For all three metals, higher coverage values were obtained for the longer (phenylacetylene)n linker (n = 2) than for the shorter (n = 1).

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