| Self-assembled monolayers (SAMs) containing pendant redox-active sites have received a great deal of attention over the past ten years. The investigations reported here focus on a new, more versatile family of these SAMs based on complexes of the type [Ru(Menbpp)(R2mal)(L)] + where Menbpp is 2,6-Bis(N-pyrazolyl)pyridine and its methyl substituted derivatives, R2mal is a β-diketonate, and L is a nitrile or pyridine ligand containing a pendant thiol group. Stable surfaces were achieved with the nitrile complexes, and were characterized electrochemically. In these surface studies, it was discovered that the electrode preparation and rinsing are of critical importance. In particular, appropriate rinsing procedures are required in order to distinguish between chemisorbed and physisorbed materials.; In addition, it has been demonstrated that solution based redox couples can be used to probe the nature of organic SAMs on electrode surfaces. In particular, organic thiol and disulfide monolayers (assumed in the literature to provide identical monolayers) display different responses to these solution redox species. Specifically, alkyl-thiols show good blocking behavior (“blocking” indicates that the electrode shows no response due to the solution couple), while alkyl-disulfides often give SAMs with somewhat less effective blocking and less reproducible results. These experiments also demonstrate that when using the observation of solution redox couples as a measure of SAM surface integrity, one must consider the charge of the complex, and the ability of the complex to partition into the intact monolayer is of critical importance.; Finally, a rare example of an asymmetrically coordinated organic disulfide complex was synthesized and characterized, and the mode of disulfide coordination was confirmed by x-ray crystallography. This complex exhibits an unusually short Ru-S bond and a high Ru(III/II) potential consistent with the disulfide exhibiting a high degree of π-acidity towards the ruthenium(II) center. |
