Long-Range Ferromagnetic Exchange Interactions Mediated by Mn-CeIV-Mn Superexchange Involving Empty 4f Orbitals

Sayak Das Gupta; Robert L Stewart; Dian-Teng Chen; Khalil A Abboud; Hai-Ping Cheng; Stephen Hill; George Christou

doi:10.1021/acs.inorgchem.0c00332

Long-Range Ferromagnetic Exchange Interactions Mediated by Mn-Ce^IV-Mn Superexchange Involving Empty 4f Orbitals

Inorg Chem. 2020 Jul 6;59(13):8716-8726. doi: 10.1021/acs.inorgchem.0c00332. Epub 2020 Jun 23.

Authors

Sayak Das Gupta¹, Robert L Stewart², Dian-Teng Chen³, Khalil A Abboud¹, Hai-Ping Cheng³, Stephen Hill², George Christou¹

Affiliations

¹ Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States.
² National High Magnetic Field Laboratory and Department of Physics, Florida State University, Tallahassee, Florida 32310, United States.
³ Department of Physics, University of Florida, Gainesville, Florida 32611, United States.

PMID: 32573216
DOI: 10.1021/acs.inorgchem.0c00332

Abstract

Reactions involving reductive aggregation of MnO₄^- in methanol in the presence of Ce^IV and an excess of carboxylic acid have led to the synthesis of structurally related Ce/Mn clusters, [Ce₃Mn₅O₈(OMe)(O₂CBu^t)₁₃(MeOH)] (1) and [Ce₂Mn₃O₅(O₂CPh)₉(MeOH)₃] (2), containing at least one {Mn₂Ce₂O₄} cubane unit. The cores of both clusters contain Mn_x units separated by three (1) or two (2) Ce^IV ions. Fits of variable-temperature, solid-state dc and ac magnetic susceptibility data reveal dominant ferromagnetic interactions within 1 and 2, resulting in the maximum S = ¹⁷/₂ and S = 5 ground state spins, respectively, and thus suggesting significant ferromagnetic (F) interactions between the Mn_x units that are ≥6 Å apart and separated by four intervening bonds through diamagnetic Ce^IV. Fits of magnetic susceptibility data also revealed unusual long-range F interactions, and this finding was further supported by high-field EPR measurements and simulations. Density functional theory calculations and a Wannier function analysis confirm long-range interactions and indicate a Mn-Ce-Mn superexchange pathway via Mn-d/Ce-f orbital overlap/hybridization.