Ligand-Controlled Magnetic Interactions in Mn4 Clusters

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 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.