Ethyl disulfide possessing two nickel(II) pentaazamacrocyclic redox centers at its end carbon atoms, 1, adsorbs on gold electrodes from methanol solutions and yields stable, electroactive self-assembled monolayers (SAMs). Cyclic voltammetry of SAMs of 1 shows a stable redox wave at 0.55 V in aqueous 0.1 M Na2SO4 (pH 2), corresponding to the Ni2+/3+ redox reaction. For SAME of 1 with the surface coverage (Gamma) of nickel(II) redox centers of(1.41 +/- 0.04) x 10(-10) mol cm(-2) the cyclic voltammograms (CV) show very small peak-to-peak separations (Delta E-p < 20 mV) with the Delta E-fwhm (full-width at half-maximum of CV peaks) values ranging from 140 to 150 mV, indicating electrostatic repulsive interactions among the surface-immobilized nickel(II) redox centers. The constructed SAM of 1 was defined as a square close-packed monolayer with the polyazamacrocyclic ring of the nickel(II) redox center oriented perpendicular to the electrode surface. Coadsorption of 1 with electroinactive alkyl/aryl disulfides furnishes mixed monolayers, and the Gamma of the electroactive nickel(II) redox centers can be varied by the mole ratio of 1 and coadsorbate in the adsorption solution. In mixed monolayers, the Delta E-fwhm decreases as the Gamma of 1 decreases from the limiting monolayer surface coverage, suggesting a homogeneous distribution of 1 and coadsorbate in the constructed mixed monolayers. The formal potentials (E degrees＇) of the solution-dissolved 1 and the self-assembly of 1 with different Gamma values, equivalent to 0.3-1 monolayer, are nearly equal, evidencing the same microenvironment around the nickel(II) redox centers in both the self-assembly and the solution phase. Exchange between the surface-immobilized gold-alkanethiolates with disulfides in solution has been observed and was found to accompany ordering of the monolayer. The apparent rate constant for the heterogeneous electron-transfer reaction, k(app), has been determined by fast-scan cyclic voltammetry to be 1.3 x 10(3) s(-1) for the SAM of 1. An increase in the k(app) with a decrease in the Gamma of 1 in mixed monolayers was observed.