Single-Molecule Magnet Behavior and Spin Structure of an Fe^III₇ Cartwheel Cluster Revealed by Sub-Kelvin Magnetometry and Mössbauer Spectroscopy: The Final Pieces of the Puzzle

Bartolomé, Juan ; Bartolomé, Elena ; Luis, Fernando ; Burzurí, Enrique ; Camón, Agustin ; Filoti, George ; Ako, Ayuk M. ; Braun, Jonas ; Mereacre, Valeriu ; Anson, Christopher E. ; Powell, Annie K.

Resumen: The spin frustration and other magnetic properties of the “cartwheel” heptanuclear cluster [FeIII7O3(O2CtBu)9(Me-dea)3(H2O)3] (Me-deaH2 = N-methyldiethanolamine) have been previously investigated; we present here a Mössbauer spectroscopic study and sub-Kelvin magnetization and ac susceptibility measurements which enable a complete magnetic picture of this frustrated cluster. 57Fe Mössbauer spectra above 150 K showed three doublets in a 1:3:3 ratio, which could be assigned by their respective quadrupole splittings to the central Fe(1) and the peripheral Fe(2) and Fe(3). The field dependence of the corresponding magnetic sextets at 3 K showed that the spins on the central Fe(1) and the three peripheral Fe(2) sites with O5N coordination are oriented mutually coparallel, while these are antiparallel to the spins on the peripheral Fe(3) sites with O6 coordination, resulting in an overall S = 5/2 ground state. This provides experimental confirmation of the previously proposed spin ground state structure. Upon cooling to sub-Kelvin temperatures, a crossover to spin blocking with TB ≈ 0.21 K could be observed. This single-molecule magnet behavior had been expected but had not been observable with a conventional SQUID. The anisotropy barrier, of 3-fold symmetry, can be described in terms of the parameter D/kB = −0.47 K and a fourth-order perturbation; the latter enables thermally activated quantum tunneling through the excited sublevel mz = ± 3/2, with an activation barrier of U/kB = 1.9 K.

Idioma: Inglés

DOI: 10.1021/acs.inorgchem.4c04191

Año: 2024

Publicado en: Inorganic Chemistry 63, 51 (2024), 24262-24273
ISSN: 0020-1669

Factor impacto JCR: 4.7 (2024)

Categ. JCR: CHEMISTRY, INORGANIC & NUCLEAR rank: 6 / 42 = 0.143 (2024) - Q1 - T1

Factor impacto SCIMAGO: 0.958 - Chemistry (miscellaneous) (Q1) - Physical and Theoretical Chemistry (Q1) - Inorganic Chemistry (Q1)

Financiación: info:eu-repo/grantAgreement/ES/AEI/CEX2023-001263-S
Financiación: info:eu-repo/grantAgreement/ES/AEI/CEX2023-001286-S
Financiación: info:eu-repo/grantAgreement/ES/AEI/AEI PID2022-140923NB-C21
Financiación: info:eu-repo/grantAgreement/ES/AEI/AEI PID2022-140923NB-C22
Financiación: info:eu-repo/grantAgreement/ES/DGA/E09-17R-Q-MAD
Financiación: info:eu-repo/grantAgreement/ES/DGA-FSE/E12-23R-RASMIA
Financiación: info:eu-repo/grantAgreement/ES/MICINN-AEI/PRTR-C17.I1
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PID2022-138492NB-I00

Tipo y forma: Artículo (Versión definitiva)