A Ligand Field Series for the 4f-Block from Experimental and DFT Computed Ce(IV/III) Electrochemical Potentials

Understanding of the sensitivity
of the reduction potential of cerium­(IV) cations to ligand field strength
has yet to benefit from systematic variation of the ligand environment.
Detailed analyses for a series of seven cerium­(IV) tetrakis­(pyridyl-nitroxide)
compounds and their cerium­(III) analogues in varying ligand field
strengths are presented. Electrochemical, spectroscopic, and computational
results reveal a close correlation of electronic properties with ligand
substituents. Together with electrochemical data for reported eight-coordinate
compounds, DFT calculations reveal a broad range of the cerium­(IV/III)
redox potentials correlated to ligand field strengths, establishing
a semiempirical, predictive model for the modulation of cerium redox
thermodynamics and ligand field strengths. Applications over a variety
of scientific disciplines make use of the fundamental redox thermodynamics
of cerium. Such applications will benefit from a combined experimental
and theoretical approach for assessing redox cycling of cerium compounds.