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.