Magnetic Properties of Two New Fe4 Single‐Molecule Magnets in the Solid State and in Frozen Solution |
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| Authors: | Christoph Schlegel Dr. Enrique Burzurí Fernando Luis Dr. Fabrizio Moro Maria Manoli Dr. Euan K. Brechin Dr. Mark Murrie Dr. Joris van Slageren Dr. |
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| Affiliation: | 1. 1. Physikalisches Institut, Universit?t Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany);2. Instituto de Ciencia de Materiales de Aragón, CSIC‐Universidad de Zaragoza, 50009 Zaragoza (Spain);3. School of Chemistry, University of Nottingham, Nottingham, NG7 2RD (UK), Fax: (+44)?1159513563;4. School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JJ (UK);5. Department of Chemistry, The University of Glasgow, University Avenue Glasgow G12 8QQ (UK) |
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| Abstract: | Two novel tetranuclear, star‐shaped iron(III) clusters, [Fe4(acac)6(Br‐mp)2] and [FeIII4(acac)6(tmp)2], are described. Both have S=5 ground states resulting from antiferromagnetic nearest‐neighbour superexchange interactions, with J=?8.2 cm?1 and J=?8.5 cm?1 for 1 and 2 , respectively. Energy barriers for the relaxation of the magnetisation of approximately 12 cm?1 were derived from AC susceptibility measurements. Magnetic resonance measurements revealed a zero‐field splitting parameter D=?0.34 cm?1 for both complexes. AC susceptibility measurements in solution demonstrated that the complexes are reasonably stable in solution. Interestingly, the magnetisation relaxation slows down significantly in frozen solution, in contrast to what is generally observed for single‐molecule magnets. This was shown to result from a large increase in τ0, the prefactor in the Arrhenius equation, with the energy barrier remaining unchanged. |
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| Keywords: | cluster compounds EPR spectroscopy magnetic properties magnetisation relaxation molecular magnetism |
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