Evidence of proton-coupled mixed-valency by electrochemical behavior on transition metal complex dimers bridged by two Ag ions

H-Bonded metal complex dimers with reversible redox behaviour, which are connected by a low-barrier hydrogen bond (LBHB) with a very low energy barrier for proton transfer, can provide a unique mixed-valency state stabilized by the proton-coupled electron transfer (PCET) phenomenon. Using cyclic vol...

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Bibliographic Details
Published in:Dalton transactions : an international journal of inorganic chemistry 2019-01, Vol.48 (2), p.535-546
Main Authors: Tadokoro, Makoto, Isogai, Kazuo, Harada, Shohei, Kouchi, Takaya, Yamane, Takeshi, Sugaya, Tomoaki, Kamebuchi, Hajime
Format: Article
Language:English
Subjects:
Coordination compounds
Crystallography
Dichloromethane
Dimers
Electrochemical analysis
Electron transfer
Electrons
Hydrogen bonds
Protons
Silver
Transition metal compounds
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Summary:H-Bonded metal complex dimers with reversible redox behaviour, which are connected by a low-barrier hydrogen bond (LBHB) with a very low energy barrier for proton transfer, can provide a unique mixed-valency state stabilized by the proton-coupled electron transfer (PCET) phenomenon. Using cyclic voltammetry measurements, newly prepared [Re III Cl 2 (P n Pr 3 ) 2 (Hbim)] 2 ( 2 ) and [Os III Cl 2 (P n Pr 3 ) 2 (Hbim)] 2 ( 3 ) existing as H-bonded dimers in a CH 2 Cl 2 solution showed a four-step and four-electron transfer containing two mixed-valency states of Re II Re III and Re III Re IV , and Os II Os III and Os III Os VI , respectively. Furthermore, [Re III Cl 2 (P n Pr 3 ) 2 (Agbim)] 2 ( 4 ) and [Os III Cl 2 (P n Pr 3 ) 2 (Agbim)] 2 ( 5 ), bridged by two Ag + ions instead of two H-bonding protons, were prepared, and their electrochemical behaviours changed to a two-step and four-electron transfer. It is clear that the H-bonded complex dimers 2 and 3 , connected by an LBHB, can be electrochemically stabilized into unique pairs of mixed-valency states by PCET, and the H-bonding proton transfer also controls the electrochemical redox behaviour. H-Bonded metal complex dimers with reversible redox behavior connected by an LBHB can provide a unique mixed-valency state. However, the metal complexes substituted two H-bonding protons to two Ag + ions electrochemically have no mixed-valency state.
ISSN:1477-9226
1477-9234
DOI:10.1039/c8dt03962c