Slow Magnetic Relaxation and Electron Delocalization in an S = 9/2 Iron(II/III) Complex with Two Crystallographically Inequivalent Iron Sites

Author

Susanta Hazra
Sujit Sasmal
Michel Fleck
Fernande Grandjean, Missouri University of Science and TechnologyFollow
Moulay T. Sougrati
Meenakshi Ghosh
T. David Harris
Pierre Bonville
Gary J. Long, Missouri University of Science and TechnologyFollow
Sasankasekhar Mohanta

Abstract

The magnetic, electronic, and Mössbauer spectral properties of Fe ₂L(µ-OAc)₂ClO₄, 1, where L is the dianion of the tetraimino-diphenolate macrocyclic ligand, H₂L, indicate that 1 is a class III mixed valence iron(II/III) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a [Fe₂]^V cationic configuration with a S_t 9/2 ground state. Fits of the dc magnetic susceptibility between 2 and 300K and of the isofield variable-temperature magnetization of 1 yield an isotropic magnetic exchange parameter, J, of -32(2) cm^-1 for an electron transfer parameter, B, of 950 cm^-1, a zero-field uniaxial D_9/2 parameter of -0.9(1) cm^-1, and g 1.95(5). In agreement with the presence of uniaxial magnetic anisotropy, ac susceptibility measurements reveal that 1 is a single-molecule magnet at low temperature with a single molecule magnetic effective relaxation barrier, U_eff, of 9.8 cm^-1. At 5.25 K the Mössbauer spectra of 1 exhibit two spectral components, assigned to the two crystallographically inequivalent iron sites with a static effective hyperfine field; as the temperature increases from 7 to 310 K, the spectra exhibit increasingly rapid relaxation of the hyperfine field on the iron-57 Larmor precession time of 5 x 10^-8 s. A fit of the temperature dependence of the average effective hyperfine field yields |D_9/2| 0.9 cm^-1. An Arrhenius plot of the logarithm of the relaxation frequency between 5 and 85 K yields a relaxation barrier of 17 cm^-1.

Recommended Citation

S. Hazra and S. Sasmal and M. Fleck and F. Grandjean and M. T. Sougrati and M. Ghosh and T. D. Harris and P. Bonville and G. J. Long and S. Mohanta, "Slow Magnetic Relaxation and Electron Delocalization in an S = 9/2 Iron(II/III) Complex with Two Crystallographically Inequivalent Iron Sites," Journal of Chemical Physics, vol. 134, no. 17, American Institute of Physics (AIP), May 2011.

The definitive version is available at https://doi.org/10.1063/1.3581028

Department(s)

Chemistry

Keywords and Phrases

Ac-susceptibility Measurements; DC Magnetic Susceptibility; Dianions; Electron Delocalization; Electron Transfer; Hyperfine Field; Larmor Precession; Low Temperatures; Macro-cyclic Ligands; Magnetic Exchange; Mixed Valence; Rapid Relaxation; Relaxation Frequency; Single Molecule; Single-molecule Magnet; Spectral Components; Spectral Properties; Temperature Dependence; Temperature Increase; Uniaxial Magnetic Anisotropy; Variable Temperature; Zero Fields; Algebra; Arrhenius Plots; Iron; Magnetic Anisotropy; Magnetic Susceptibility; Magnetism; Iron Compounds; Ferric Ion; Ferrous Ion; Chemical Structure; Chemistry; Electron; Magnetism; Mössbauer Spectroscopy; X Ray Crystallography; Crystallography; X-Ray; Electrons; Ferric Compounds; Ferrous Compounds; Magnetics; Models; Molecular; Spectroscopy; Mössbauer

International Standard Serial Number (ISSN)

0021-9606

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2011 American Institute of Physics (AIP), All rights reserved.

Publication Date

01 May 2011