Charge and Solvent Effects on the Redox Behavior of Vanadyl Salen-Crown Complexes
Issued Date
2023-01-01
Resource Type
ISSN
10895639
eISSN
15205215
Scopus ID
2-s2.0-85163473215
Journal Title
Journal of Physical Chemistry A
Rights Holder(s)
SCOPUS
Bibliographic Citation
Journal of Physical Chemistry A (2023)
Suggested Citation
Nguyen H.M., Morgan H.W.T., Chantarojsiri T., Kerr T.A., Yang J.Y., Alexandrova A.N., Léonard N.G. Charge and Solvent Effects on the Redox Behavior of Vanadyl Salen-Crown Complexes. Journal of Physical Chemistry A (2023). doi:10.1021/acs.jpca.3c00827 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/87956
Title
Charge and Solvent Effects on the Redox Behavior of Vanadyl Salen-Crown Complexes
Author's Affiliation
Other Contributor(s)
Abstract
The incorporation of charged groups proximal to a redox active transition metal center can impact the local electric field, altering redox behavior and enhancing catalysis. Vanadyl salen (salen = N,N′-ethylenebis(salicylideneaminato)) complexes functionalized with a crown ether containing a nonredox active metal cation (V-Na, V-K, V-Ba, V-La, V-Ce, and V-Nd) were synthesized. The electrochemical behavior of this series of complexes was investigated by cyclic voltammetry in solvents with varying polarity and dielectric constant (ϵ) (acetonitrile, ϵ = 37.5; N,N-dimethylformamide, ϵ = 36.7; and dichloromethane, ϵ = 8.93). The vanadium(V/IV) reduction potential shifted anodically with increasing cation charge compared to a complex lacking a proximal cation (ΔE1/2 > 900 mV in acetonitrile and >700 mV in dichloromethane). In contrast, the reduction potential for all vanadyl salen-crown complexes measured in N,N-dimethylformamide was insensitive to the magnitude of the cationic charge, regardless of the electrolyte or counteranion used. Titration studies of N,N-dimethylformamide into acetonitrile resulted in cathodic shifting of the vanadium(V/IV) reduction potential with increasing concentration of N,N-dimethylformamide. Binding constants of N,N-dimethylformamide (log(KDMF)) for the series of crown complexes show increased binding affinity in the order of V-La > V-Ba > V-K > (salen)V(O), indicating an enhancement of Lewis acid/base interaction with increasing cationic charge. The redox behavior of (salen)V(O) and (salen-OMe)V(O) (salen-OMe = N,N′-ethylenebis(3-methoxysalicylideneamine) was also investigated and compared to the crown-containing complexes. For (salen-OMe)V(O), a weak association of triflate salt at the vanadium(IV) oxidation state was observed through cyclic voltammetry titration experiments, and cation dissociation upon oxidation to vanadium(V) was identified. These studies demonstrate the noninnocent role of solvent coordination and cation/anion effects on redox behavior and, by extension, the local electric field.