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RESEARCH PRODUCT

Restricting Magnetic Interaction Pathways in Polyoxometalate Salts of Cationic Nitronyl Nitroxide Free Radicals

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Abstract : Salts 1 and 2 that combine the [W 6 O 19 ] 2- Lindqvist anion with the cationic nitronyl nitroxide (NN) free radicals p -MepyNN + and n Bu 3 NCH 2 NN + , respectively, have been synthesized and their structural and magnetic properties have been studied. Keywords: Nitroxide radicals, polyoxometalates, magnetism. Introduction Ferromagnetism based on purely organic materials has raised a lot of interest during the last decade [1]. Most of the studies have been performed with nitronyl nitroxide (NN) radicals due to their persistence, stability and ease of functionalization [2]. Bulk ferromagnetism in these compounds arises from ferromagnetic interactions between open-shell molecules in the solid state. For a proper design of such materials, chemists need control over 1) the organization of molecules in the solid state and 2) the sign of magnetic interactions between neighbouring molecules. The first problem has been addressed by using the concepts of crystal engineering [3]. Thus, hydrogen bonding and other types of non-covalent interactions have been used to create specific crystal packings by design [4]. The second aspect is more delicate to control since the prediction of the type of interaction (ferro or antiferromagnetic) has not been solved to date. Usually, ferromagnetic interactions have been ascribed to intermolecular contacts between atoms carrying spin densities of opposite signs (McConnell I proposal) [5]. This model is an easy-to-use tool, since spin densities can be obtained experimentally (NMR or polarized neutron diffraction methods) in the solid state [6]. However, it has been shown that