title: Magnetic properties of two new Fe(4) single-molecule magnets in the solid state and in frozen solution.
abstract: Two novel tetranuclear, star-shaped iron(III) clusters, [Fe(4)(acac)(6)(Br-mp)(2)] and [Fe(III) (4)(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 tau(0), the prefactor in the Arrhenius equation, with the energy barrier remaining unchanged.
authors.affiliation: 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schlegel
authors.forename: Enrique
authors.initials: E
authors.lastname: Burzurí
authors.forename: Fernando
authors.initials: F
authors.lastname: Luis
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Moro
authors.forename: Maria
authors.initials: M
authors.lastname: Manoli
authors.forename: Euan K
authors.initials: EK
authors.lastname: Brechin
authors.forename: Mark
authors.initials: M
authors.lastname: Murrie
authors.forename: Joris
authors.initials: J
authors.lastname: van Slageren