E. Kampert, F.F.B.J. Janssen, D.W.
Boukhvalov, J.C. Russcher, J.M.M. Smits, R. de Gelder, B. de Bruin,
P.C.M. Christianen, U. Zeitler, M.I, Katsnelson, J.C. Maan, A.E. Rowan,
Ligand-controlled
magnetic interactions in Mn4 clusters,
Inorg. Chem. 48 (2009) 11903-11908
Abstract:
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 Mn-4 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 (J(1), J(2), and J(3)) present between the
metal ions Experimentally measured magnetic moments in high magnetic
fields show that, upon electron density withdrawal, the main
antiferromagnetic exchange constant J(1) decreases from -2.2 K for the
[Mn-4(OAc)(4)] cluster to -1.9 K for the [Mn-4(H5C6COO)(4)] cluster and
-0.6 K for the [Mn-4(F3CCOO)(4)] cluster, while J(2) decreases from -1
1 K to nearly 0 K and J(3) 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 [Mn-4(OAc)(4)] and [Mn-4(F3CCOO)(4)]
clusters.