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Ligand-Controlled Magnetic Interactions in Mn4 Clusters

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posted on 21.12.2009, 00:00 by Erik Kampert, Femke F. B. J. Janssen, Danil W. Boukhvalov, Jaap C. Russcher, Jan M. M. Smits, René de Gelder, Bas de Bruin, Peter C. M. Christianen, Uli Zeitler, Mikhail I. Katsnelson, Jan C. Maan, Alan E. Rowan
A method is presented to design magnetic molecules in which the exchange interaction between adjacent metal ions is controlled by electron density withdrawal through their bridging ligands. We synthesized a novel Mn4 cluster in which the choice of the bridging carboxylate ligands (acetate, benzoate, or trifluoroacetate) determines the type and strength of the three magnetic exchange couplings (J1, J2, and J3) present between the metal ions. Experimentally measured magnetic moments in high magnetic fields show that, upon electron density withdrawal, the main antiferromagnetic exchange constant J1 decreases from −2.2 K for the [Mn4(OAc)4] cluster to −1.9 K for the [Mn4(H5C6COO)4] cluster and −0.6 K for the [Mn4(F3CCOO)4] cluster, while J2 decreases from −1.1 K to nearly 0 K and J3 changes to a small ferromagnetic coupling. These experimental results are further supported with density-functional theory calculations based on the obtained crystallographic structures of the [Mn4(OAc)4] and [Mn4(F3CCOO)4] clusters.

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