I understand that the presence of pi-conjugation in coordinating ligands traps the incoming electron and participates in redox event and interferes with the metal-redox. The question is, would the redox-active ligand hold the electron or would it transfer to the metal? If anyone have relevant references, for instance, the initial ligand reduction followed by an electron transfer to the metal centre case, provide me the article links.
Thank you.
I do not know if I get correctly your question, but I believe there is not a simple answer. What you are comparing is the redox behaviour of a solvated metal ion with a complex of the same metal with redox-active ligands. A typical example is represented by bis(1,2-dithiolene) complexes. Dithiolene ligands are themselves redox-active species (and can carry charges ranging between -2, in dithiolates, and 0, in dithiones). Their complexes, say with metal ions such as Ni(II), are also redox active. This said, the redox potentials of the complexes are not directly related to those of the "free" (solvated) metal ions. A comparison can be done theoretically by comparing the absolute reduction potentials, which in turn are obtained from thermochemical data. Some of these concepts can be found in a recent paper we published on the diradical character of such ligands (Article Diradical Character of Neutral Heteroleptic Bis(1,2-dithiole...
). I hope this may help!
Thank you for your article. I would like to reword my question.
Lets say that we have a metal complex having a pi-conjugate ligand in its coordination sphere, when a one-electron reduction of this complex is carried out , initially the ligand gets the incoming electron, later it transfers the electron to the metal centre. It's been argued that the later is thermodynamically a favourable process. How one can confirm these processes experimentally, in particular, the second step of electron transfer from the ligand to the metal centre? Are there examples available in the literature?
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electron transfer books
The most commonly used techniques to investigate redox process are electrochemical measurements, and cyclic voltammetry (CV) in particular. A comparison between the redox potentials of free ligands and the metal complex can give useful hints on which part of the molecule is involved in the redox process. CV is often accompanied by differential pulse voltammetry (DPV), that allows a direct estimation of the number of electrons involved in the process. Finally, EPR in many case can indicate a change in the oxidation state of the metal. Hence, a joined CV/DPV/EPR approach can guide the researcher in understanding the mechanism underlying a complex redox step.
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