Spectroelectrochemistry as a Tool to Identify Redox Sites

Several complexes offer two or more redox-active moieties that may undergo electron transfer at rather similar potentials. In such cases voltammetric or potentiometric techniques alone may not suffice to unambiguously assign individual redox processes or to elucidate the order of redox events within such molecules. If, however, the individual redox-active constituents generate oxidised or reduced forms with clearly distinguishable spectroscopic properties, a suitable combination of electrochemical and spectroscopic investigations can 

Heterodimetallic complexes with fully conjugated oligoynediyl or diethynyl arene bridges constitute another interesting family of compounds where an assignment of individual redox sites may not be trivial. In these systems, strong 

Chart 6.1 Allenylidene complexes with redox-active substituents and ligands. 

In tra 5-[Cl(dppm)2Ru = C = C = C(SeFc)(C2H4CH = CH2)], the redox-active ferrocenyl substituent is directly attached to the allenylidene ligand. Oxidation of the ferrocenylselenyl group caused a redshift of the allenylidene IR band by 10 cm This result fully conforms to what one would expect of the replacement of a substituent ER by a weaker donor. Such substitution 

Spectroelectrochemistry has also allowed discrimination between metal- or ligand-dominated oxidations in the 1,3-divinylphenylene-bridged diruthenium 

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