Synthesis and Characterization of Redox-Active Metal Complexes Sequentially Self-Assembled onto Gold Electrodes via a New Thiol−Terpyridine Ligand

Abstract

We report on the synthesis of a new thiol-modified terpyridine ligand 4‘-(5-mercaptopentyl)-2,2‘:6‘,2‘‘-terpyridinyl (tpy − SH) as well as of its complexes with Co, Cr, and Os. We have prepared complexes of the type [M(tpy − SH)2] n + and [M(tpy − SH)L] n + (L = terpyridine, tetrapyridylpyrazine (tppz)). The free ligand as well as the tpy − SH-containing metal complexes adsorb strongly onto gold electrode surfaces, and in the case of the metal complexes, they retain their redox-active responses at potentials very close to those of nonadsorbing analogs in homogeneous solution. In the case of [Co(tpy − SH)(tpy)]2+ adsorbed onto a gold electrode surface, the cyclic voltammetric response exhibits an aging process where it sharpens significantly over long times (days), suggesting a slow reorganization of the adsorbed complex on the electrode surface. Reaction with CoCl2 of a gold electrode whose surface had been previously modified with the tpy − SH ligand ostensibly gives rise to Au/S−tpy−CoCl2. Upon cycling the potential of such a modified electrode over the potential region of +0.40 to −0.40 V, we observe a voltammetric wave at about −0.20 V which initially decreases rapidly with time but much more slowly afterward. Concomitantly, a new reversible voltammetric wave appears at +0.13 V which we ascribe to the formation of the surface-immobilized [Co(tpy − SH)2]2+ complex via a surface chelate formation (Au−S−tpy−Co−tpy−S−Au). The presence of sharp isopotential points suggests a simple transformation between these two surface species. Gold electrodes could also be modified with [Os(tpy − SH)(tpy)]2+ which, as in the case of the analogous cobalt complex, exhibited a redox wave associated with the surface immobilized complex at a potential very similar to that of [Os(tpy)2]2+ in solution. Reaction of a gold electrode surface, previously modified with [Os(tpy − SH)tppz]2+, with [Co(tppz)(Cl)2] gives rise to the appearance of a new voltammetric wave at +0.26 V, which we ascribe to binding of the cobalt to the pendant tppz to give rise to a structured interface of the type Au−S−tpy−Os−tppz−Co−tppz. An electrode modified with a layer of [Cr(tpy − SH)2]3+ exhibits electrocatalytic behavior toward the reduction of nitric oxide (NO) in solution.

EQCM Characterization of Self-Assembled Kinetics of 4-Pyridyl Hydroquinone at Pt Surface and Its Ion Transfer in Electrochemical Redox

“…In the ideal cyclic voltammogram for a surface-con®ned species, the full width at half-maximum (DE fwhm ) is given by DE fwhm 90X6an mV such an ideal behavior is often not observed in experiments. Our results (DE fwhm 138 mV in oxidation process, and 134 mV in reduction process at 100 mVas) are well above the theoretical value and different from other articles [23,24].…”

“…The decrease resulted from the emigration of hydrate hydrogens during the oxidation of hydroquinone process. Such a behavior has been reported previously [24,26].…”

Terpyridine‐Functionalized Surfaces: Redox‐Active, Switchable, and Electroactive Nanoarchitecturesgland

“…[ 11 ] For this purpose, the complex [Cr( 1 ) 2 ] 3 + was selfassembled onto Au electrodes (for the electrochemical reduction of CO 2 and NO catalyzed by terpyridine complexes, see ref. [25,26]).…”

“…[ 5 ] These types of SAMmodifi ed surfaces are highly useful for investigating fundamental phenomena on artifi cially designed nanostructures: e.g., distance-dependent electron-transfer processes, [ 6 ] the mechanism of single electron-transfer, [ 7 ] and the observation of quantum size effects (e.g., coulomb staircases). [ 8 ] Moreover, monolayers on metallic or semiconducting surfaces are also of relevance for several applications, including (bio)chemical sensing, [9][10][11] control of surface properties (e.g., wettability and friction), [ 12 ] corrosion protection, [ 13 , 14 ] patterning, [ 15 , 16 ] semiconductor passivation, [ 17 ] and/or nonlinear optics. [ 18 ] Molecular engineering represents an interdisciplinary area, where supramolecular systems have to be capable of performing electronic operations such as switching, gating, rectification, or amplifi cation, thus, new systems have to be developed.…”

Encoding Molecular‐Wire Formation within Nanoscale Sockets

“…[29,30,33] For the monolayers that are terminated with terpyridyl units, we chose transition-metal ions to connect the two ends through well-known coordination chemistry (Figure 1 b). [34,35] Cobalt ions, in particular, are attractive because their complexes are readily formed at room temperature with a variety of terpyridyl ligands. [35] We also studied aldehyde-terminated bisoxazole monolayers and their reactions with aromatic amines (Figure 1 c).…”