TY - JOUR
T1 - Slow magnetic relaxation and electron delocalization in an S 92 iron(IIIII) complex with two crystallographically inequivalent iron sites
AU - Hazra, Susanta
AU - Sasmal, Sujit
AU - Fleck, Michel
AU - Grandjean, Fernande
AU - Sougrati, Moulay T.
AU - Ghosh, Meenakshi
AU - Harris, T. David
AU - Bonville, Pierre
AU - Long, Gary J.
AU - Mohanta, Sasankasekhar
N1 - Funding Information:
The authors thank Professor J. R. Long for the use of the SQUID magnetometer, Professor Charles E. Johnson for helpful discussions during the course of this work, and Dr. R. P. Hermann for help with some programming code. Financial support from the Government of India through the Department of Science and Technology (grants SR/S1/IC-12/2008), the Council for Scientific and Industrial Research for a fellowship to S.H., the University Grants Commission for a Fellowship to S.S., and the Fonds National de la Recherche Scientifique, Belgium (grants 9.456595 and 1.5.064.05) is gratefully acknowledged.
PY - 2011/5/7
Y1 - 2011/5/7
N2 - The magnetic, electronic, and Mssbauer spectral properties of Fe 2L(-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(IIIII) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a Fe2V cationic configuration with a St 92 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 D92 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 Mssbauer 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 |D92| 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.
AB - The magnetic, electronic, and Mssbauer spectral properties of Fe 2L(-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(IIIII) complex with an electron that is fully delocalized between two crystallographically inequivalent iron sites to yield a Fe2V cationic configuration with a St 92 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 D92 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 Mssbauer 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 |D92| 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.
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U2 - 10.1063/1.3581028
DO - 10.1063/1.3581028
M3 - Article
C2 - 21548699
AN - SCOPUS:79957525130
VL - 134
JO - Journal of Chemical Physics
JF - Journal of Chemical Physics
SN - 0021-9606
IS - 17
M1 - 174507
ER -