Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites
- Author(s)
- Susanta Hazra, Sujit Sasmal, Michel Fleck, Fernande Grandjean, Moulay T. Sougrati, Meenakshi Ghosh, T. David Harris, Pierre Bonville, Gary J. Long
- Abstract
The magnetic, electronic, and Mössbauer spectral properties of [Fe2L(μ-OAc)2]ClO4, 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 St = 9/2 ground state. Fits of the dc magnetic susceptibility between 2 and 300 K 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 D9/2 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, Ueff, 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 × 10−8 s. A fit of the temperature dependence of the average effective hyperfine field yields |D9/2| = 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.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- University of Calcutta, Université de Liège, Max-Planck-Institut für bioanorganische Chemie, University of California, Berkeley, French Alternative Energies and Atomic Energy Commission (CEA), Missouri State University
- Journal
- Journal of Chemical Physics
- Volume
- 134
- Pages
- 1-13
- No. of pages
- 13
- ISSN
- 0021-9606
- Publication date
- 2011
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/10ad854e-6b42-4db9-ab7e-541fd7fbebe6