Elucidation of the Structure of a Thiol Functionalized Cu-tmpa Complex Anchored to Gold via a Self-Assembled Monolayer

[Image: see text] The structure of the copper complex of the 6-((1-butanethiol)oxy)-tris(2-pyridylmethyl)amine ligand (Cu-tmpa-O(CH(2))(4)SH) anchored to a gold surface has been investigated. To enable covalent attachment of the complex to the gold surface, a heteromolecular self-assembled monolayer (SAM) of butanethiol and a thiol-substituted tmpa ligand was used. Subsequent formation of the immobilized copper complex by cyclic voltammetry in the presence of Cu(OTf)(2) resulted in the formation of the anchored Cu-tmpa-O(CH(2))(4)SH system which, according to scanning electron microscopy and X-ray diffraction, did not contain any accumulated copper nanoparticles or crystalline copper material. Electrochemical investigation of the heterogenized system barely showed any redox activity and lacked the typical Cu(II/I) redox couple in contrast to the homogeneous complex in solution. The difference between the heterogenized system and the homogeneous complex was confirmed by X-ray photoelectron spectroscopy; the XPS spectrum did not show any satellite features of a Cu(II) species but instead showed the presence of a Cu(I) ion in a ∼2:3 ratio to nitrogen and a ∼2:7 ratio to sulfur. The +I oxidation state of the copper species was confirmed by the edge position in the X-ray absorption near-edge structure (XANES) region of the X-ray absorption spectrum. These results show that upon immobilization of Cu-tmpa-O(CH(2))(4)SH, the resulting structure is not identical to the homogeneous Cu(II)-tmpa complex. Upon anchoring, a novel Cu(I) species is formed instead. This illustrates the importance of a thorough characterization of heterogenized molecular systems before drawing any conclusions regarding the structure–function relationships.