Dynamics of [Os(bpy)(2)(p3p)(2)](2+) adsorption and desorption on platinumand gold microelectrodes

The mechanism for the formation of monolayers of [Os(2,2 ' -bipyridyl)(2) ( 4,4 ' -trimethylenedipyridine)(2)](2+) [Os(bpy)(2) (p3p)(2)](2+) on gold an d platinum microelectrodes has been investigated by monitoring the time evo lution of the surface coverage. The monolay ers were formed in 2:1 H2O:dime thylformamide solution containing between 10 and 100 muM of the complex. Th e voltammetric response of those films corresponding to the Os2+/3+ redox r eaction is nearly ideal. Cyclic voltammetry was used to determine the surfa ce coverage vs. time profile following transfer of the modified electrode i nto aqueous perchlorate electrolyte. Monolayer formation occurs on the tens of minutes time scale and follows a second order rate law for both gold an d platinum electrodes. For gold, the rate constant is 4.6 +/- 0.5 x 10(2) M -1 s(-1) for bulk concentrations between 10 and 100 muM. In contrast, more complex behavior is observed on platinum with multilayers being formed wher e C-B exceeds approximately 20 muM The apparent rate constants for binding to platinum are at least a factor of 2 smaller than for gold. For both elec trode materials, desorption follows first order rate kinetics indicating th at the adsorbates do not interact strongly with one another. The time const ants for desorption are comparable with those found for adsorption. The fir st order desorption rate constants are 4.1 +/- 0.3 and 1.8 +/- 0.2 X 10(-5) s(-1) modified gold and platinum electrodes, respectively. (C) 2000 The El ectrochemical Society. S0013-465 1 (00)08-037-X. All rights reserved.