Slow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites

Autor(en)

Susanta Hazra, Sujit Sasmal, Michel Fleck, Fernande Grandjean, Moulay T. Sougrati, Meenakshi Ghosh, T. David Harris, Pierre Bonville, Gary J. Long

Abstrakt

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(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

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

Band

134

Seiten

1-13

Anzahl der Seiten

13

ISSN

0021-9606

Publikationsdatum

2011

Peer-reviewed

Ja

ÖFOS 2012

105113 Kristallographie

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/10ad854e-6b42-4db9-ab7e-541fd7fbebe6