Edward Mu

All Publications

• A formal FeIII/V redox couple in an intercalation electrode. Nature materials Ramachandran, H., Mu, E. W., Lomeli, E. G., Braun, A., Goto, M., Hsu, K. H., Liu, J., Jiang, Z., Lim, K., Busse, G. M., Moritz, B., Kas, J. J., Vinson, J., Rehr, J. J., Park, J., Abate, I. I., Shimakawa, Y., Solomon, E. I., Yang, W., Gent, W. E., Devereaux, T. P., Chueh, W. C. 2025

  Abstract

  Iron redox cycling between low-valent oxidation states of FeII and FeIII drives crucial processes in nature. The FeII/III redox couple charge compensates the cycling of lithium iron phosphate, a positive electrode (cathode) for lithium-ion batteries. High-valent iron redox couples, involving formal oxidation higher than FeIII, could deliver higher electrochemical potentials and energy densities. However, because of the instability of high-valent Fe electrodes, they have proven difficult to probe and exploit in intercalation systems. Here we report and characterize a formal FeIII/V redox couple by revisiting the charge compensation mechanism of (de)lithiation in Li4FeSbO6. Valence-sensitive experimental and computational core-level spectroscopy reveal a direct transition from FeIII (3d5) to a negative-charge-transfer FeV (3d5L2) ground state on delithiation, without forming FeIV, or oxygen dimers. We identify that the cation ordering in Li4FeSbO6 drives a templated phase transition to stabilize the unique FeV species and demonstrate that disrupting cation ordering suppresses the FeIII/V redox couple. Exhibiting resistance to calendar aging, high operating potential and low voltage hysteresis, the FeIII/V redox couple in Li4FeSbO6 provides a framework for developing sustainable, Fe-based intercalation cathodes for high-voltage applications.

  View details for DOI 10.1038/s41563-025-02356-x

  View details for PubMedID 41094071

  View details for PubMedCentralID 4002152

• Substituent Effects on Exchange Coupling and Magnetic Relaxation in 2,2′-Bipyrimidine Radical-Bridged Dilanthanide Complexes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Gould, C. A., Mu, E., Vieru, V., Darago, L. E., Chakarawet, K., Gonzalez, M., Demir, S., Long, J. R. 2020; 142 (50): 21197-21209

  Abstract

  Systematic analysis of related compounds is crucial to the design of single-molecule magnets with improved properties, yet such studies on multinuclear lanthanide complexes with strong magnetic coupling remain rare. Herein, we present the synthesis and magnetic characterization of the series of radical-bridged dilanthanide complex salts [(Cp*2Ln)2(μ-5,5'-R2bpym)](BPh4) (Ln = Gd, Dy; R = NMe2 (1), OEt (2), Me (3), F (4); bpym = 2,2'-bipyrimidine). Modification of the substituent on the bridging 5,5'-R2bpym radical anion allows the magnetic exchange coupling constant, JGd-rad, for the gadolinium compounds in this series to be tuned over a range from -2.7 cm-1 (1) to -11.1 cm-1 (4), with electron-withdrawing or -donating substituents increasing or decreasing the strength of exchange coupling, respectively. Modulation of the exchange coupling interaction has a significant impact on the magnetic relaxation dynamics of the single-molecule magnets 1-Dy through 4-Dy, where stronger JGd-rad for the corresponding Gd3+ compounds is associated with larger thermal barriers to magnetic relaxation (Ueff), open magnetic hysteresis at higher temperatures, and slower magnetic relaxation rates for through-barrier processes. Further, we derive an empirical linear correlation between the experimental Ueff values for 1-Dy through 4-Dy and the magnitude of JGd-rad for the corresponding gadolinium derivatives that provides insight into the electronic structure of these complexes. This simple model applies to other organic radical-bridged dysprosium complexes in the literature, and it establishes clear design criteria for increasing magnetic operating temperatures in radical-bridged molecules.

  View details for DOI 10.1021/jacs.0c10612

  View details for Web of Science ID 000600204900034

  View details for PubMedID 33322909