Electrochemistry of Multicomponent Systems. Redox Series Comprising up to 26 Reversible Reduction Processes in Polynuclear Ruthenium(II) Bipyridine-Type Complexes

Abstract

The electrochemical behavior of a family of polynuclear ruthenium(II) bipyridine-type complexes with 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) and 2,5-bis(2-pyridyl)pyrazine (2,5-dpp) as bridging ligands has been investigated in highly purified N,N-dimethylformamide solution. The compounds studied contain two, three, four, and six metal centers and have general formula [Ru n (bpy) n +2(2,X-dpp) n - 1]2 n +, where n = 2, 3, 4, or 6, X = 3 or 5, and bpy is 2,2‘-bipyridine. The wide cathodic potential window explored (up to ca. −3.1 V vs SCE) has allowed us to observe the most extensive ligand-centered redox series so far reported, comprising up to 26 reversible reduction processes for the hexanuclear complex. The redox standard potentials for overlapping processes in multielectron waves have been obtained from the analysis of the voltammetric curves and their digital simulation. The localization of each redox process and the mutual interactions of the redox centers have been elucidated through the analysis and comparison of the redox series of the various compounds. For the dinuclear species, the assignment of the redox sites has been confirmed by semiempirical molecular orbital calculations (ZINDO) and spectroelectrochemical experiments. Calculations also substantiate the important role played by bridging ligands in mediating the interactions between equivalent redox sites. Finally, it has been shown that the size of the supporting electrolyte cation has an influence on the processes occurring at the extreme cathodic region.

Spectroelectrochemical properties of homo- and heteroleptic ruthenium and osmium binuclear complexes: intercomponent communication as a function of energy differences between HOMO levels of bridge and metal centres

“…The half-wave potentials indicate that the oxidations and 40 reductions of each of the six complexes are centred on the metals and ligands, respectively. 12 The electrochemistry of the symmetric homodinuclear complex 1 is similar to that of its regioisomer [Ru(bipy) 2 (qpy)Ru(bipy) 2 ] 4+ (13a), first reported by Steel and co-workers, 34 in which the 45 bipyridyls of the BL are connected at the C4 position and not the C5 position as in the case of 1 and 2. The oxidation potential of 1 (+1.34 V vs. SCE) is 100 mV more positive than that of 13a.…”

“…8, 9 The myriad of applications are founded on the well defined chemistry of these compounds and take advantage of the versatile photophysical, 10 photochemical 11 and electrochemical 12 properties that are associ-10 ated with the metal-to-ligand charge-transfer (MLCT) excitation in these metal complexes. 13 Amongst the many multinuclear polypyridyl complexes reported, 14 an interesting subclass is represented by those binuclear systems that display additional spectroelectrochemical features 15 due to the electronic interaction between the two metal centres in the mixed valence redox state(s).…”

Unconventional Mixed‐Valent Complexes of Ruthenium and Osmium

“…The extension to higher nuclearity systems (e.g. dendrimers [108] ) and to main-group elements or organic analogues [25] or the study of "inverse" situations to Equation (1) [109,110] are developing into attractive research areas where the concepts outlined herein can be applied.…”

A Convergent Approach for the Generation of Dendrimers Containing the ­[Ru3O(CH3COO)6] Electroactive Core

“…Several dendrimeric polynuclear (polypyridine)Ru 2+ and -Os 2+ systems have already been reported in the literature. [6][7][8][9][10] From the electrochemical point of view, along with those examples, [Ru 3 O(ac) 6 (L) 3 ] n+ complexes (L = solvent or N-heterocyclic ligand) constitute appealing building blocks, since each triangular [Ru 3 O] unit displays at least four reversible redox processes in the range from -1.5 V to 2.5 V (vs. SHE). The E 1/2 values associated with each process are highly dependent on the ligand L in such a way that the choice of terminal and bridging ligands provides a suitable manner to modulate the [Ru 3 O] electrochemical properties.…”