Some evidence for the formation of an azo bond during the electroreduction of diazonium salts on Au substrates.

Molecular films obtained by electrochemical reduction of diazoniuim tetrafluoroborate salts [4-carboxybenzene (PhCOOH) and 4-amino-(2,3,5,6-tetrafluoro)-carboxybenzene (PhF(4)COOH)] on Au substrates and post-functionalization with an osmium pyridil-bipyridine complex are studied by a combination of X-ray photoelectron (XPS) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS). The spectroscopic evidence suggests the formation of N=N bonds tethering the complexes to Au. The surface coverage of the azo-bonded osmium complexes strongly depends on the electrode potential.

Electrochemical scanning tunneling spectroscopy of redox-active molecules bound by Au-C bonds.

A comparison of the electrochemical gating of molecular conduction by a redox [Os(bipyridine)(pyridine)Cl] complex tethered to Au(111) with two different metal-molecule junctions in a scanning tunneling microscope nanogap is presented. The same redox molecular structure was tethered by mercaptobenzoic acid or reduction of the aryldiazonium salt of p-aminobenzoic acid, resulting in a Au-S or Au-C bond, respectively. A two-step electron-transfer mechanism with vibrational relaxation of the redox molecule is apparent in each case.