Influence of Anions on Intervalence Charge Transfer (IVCT) in Mixed-Valence Dinuclear Complexes

Abstract

Spectroelectrochemical studies of the intervalence charge transfer (IVCT) characteristics of both diastereoisomeric forms of the dinuclear complex [{Ru(bpy)2}2(mu-dpi-)]n+ [bpy=2,2'-bipyridine; dpi-=4,5-di(2-pyridyl)imidazolate] showed that the degree of inter-metal electronic coupling (or valence delocalization) is dependent on stereochemical identity. Increasing the relative concentration of the strongly associating anion toluene-4-sulfonate in acetonitrile/[(n-C4H9)4N]{B(C6F5)4} solution differentially decreased the level of delocalization for the two diastereoisomers. In a comparative investigation of electrochemical and spectroelectrochemical techniques of the anion-induced electron localization in [{Ru(bpy)2}2(mu-dpo)]5+ [dpo=3,4-di(2-pyridyl)-1,2,5-oxadiazole], differences were observed between the two methods in the order and extent of effects induced by a number of inorganic anions (PF6-, BF4-, ClO4-). It was determined that the measure of coupling derived from electrochemical methods was less reliable than that obtained from spectral methods. Comparative electrochemical studies were undertaken on [{M(bpy)2}2(mu-BL)]n+ {M=Ru, Os; BL=dpo, dpi-), which revealed substantial differences in DeltaEox (the separation between the redox potentials for the MII-MII/MIII-MII and MII-MIII/MIII-MIII couples) for the two metal centers and therefore the comproportionation constant Kc, dependent on the neutral or anionic nature of the bridging ligand.

A “Pretender” Croconate-Bridged Macrocyclic Tetraruthenium Complex: Sizable Redox Potential Splittings despite Electronically Insulated Divinylphenylene Diruthenium Entities

“…Irrespective of the identity of the oxidation sites, the use of a croconate instead of a dicarboxylate bis(chelate) increases the thermodynamic stabilities of the mixed-valent forms as evident from the enhanced Δ E 1/2 values between the 0/+ and +/2+, or the 2+/3+ and the 3+/4+ redox couples. While the sizable effects of the anion of the supporting electrolyte point towards a significant contribution of electrostatic effects to the observed redox splittings, electrochemical studies per se are inconclusive as to whether this increase in redox splitting also entails contributions from improved electron delocalization [ 73 , 74 , 75 , 76 , 77 , 78 , 79 ]. The presence or absence of electronic coupling can, however, be probed by combining (electro)chemical oxidation with IR and UV/Vis/NIR spectroscopy, and this is the subject of the following section.…”

The shape of metallosupramolecular assemblies

“…The access to the diastereosiomeric forms gives a particular opportunity for an intimate insight into anion participation in the charge-transfer process. 52,58, 59 A study of the spectroelectrochemical study of the IVCT characteristics of rac-and meso-[{Ru(bpy) 2 } 2 (m-dpi -)] n+ {dpi -= 4,5-di(2-pyridyl)imidazolato (Fig. 2m)} 59 showed that the degree of inter-metal electronic coupling was dependent on stereochemical identity.…”

“…52,58, 59 A study of the spectroelectrochemical study of the IVCT characteristics of rac-and meso-[{Ru(bpy) 2 } 2 (m-dpi -)] n+ {dpi -= 4,5-di(2-pyridyl)imidazolato (Fig. 2m)} 59 showed that the degree of inter-metal electronic coupling was dependent on stereochemical identity. Increasing the relative concentration of the strongly-associating anion toluene-4-sulfonate in acetonitrile/[N(n-C 4 H 9 ) 4 ]{B(C 6 H 5 ) 4 } solution differentially decreased the level of electron delocalisation for the two diastereoisomers, although the extent of anion-induced localisation was modest.…”

“…The measure of delocalisation derived from electrochemical methods is less reliable than that from spectral methods, since the former method incorporates an additional contribution arising from the association of the anion with the complex. 59 This latter observation is extremely important: literature discussions regarding inter-metal communication in mixed-valence dinuclear species have often been based on electrochemical measurement of the comproportionation constant (K c ) derived from DE ox values for the particular complexes. These values may be profoundly affected by the identity of the anion used in the electrochemical experiment, rendering comparisons between different complexes very unreliable.…”

Photophysical, electrochemical, and DFT studies of the novel azacrown-bridged dinuclear ruthenium dye sensitizers for solar cells

“…The dye sensitizer is regarded as the key component which governs the photovoltaic performance of DSSCs [2]. Different strategies are adopted to optimize the performance of ruthenium bipyridyl-based complexes to fit specific functionalities, namely, employing different ancillary ligands [2], using light harvesting antennas which funnel their photonic excitation to the dye sensitizer modules [14,15], or designing spacers (bridging ligands) which separate photoactive terminals [16][17][18], among others. The role of bridging ligands is particularly attractive for they not only allow control over the spatial arrangement of the complexes but also provide an insight into the electronic coupling of the separated metal centers [19].…”