Construction of Nanosize Magnetic Bar by Assembling of Organic Molecules and Control of Their Arrangement

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Recently, there has been substantial interest in the study of molecular-based magnetism. Whereas these ferromagnetic orderings have been discovered fortuitously, methodology for designing intermolecular exchange coupling pathways has not been established yet. Organic ferromagnets so far reported have suitable arrangements to fulfill the model proposed by McConnell and/or orbital orthogonality ; however, the control of molecular arrangement in the crystal does not necessarily correspond to predictable strategy. Whereas molecular chemistry deals with the design and the synthesis of individual radical units, their assembly into a solid is governed by concepts of supramolecular chemistry. Our ultimate objective is to design radical molecules whose assembled structure can be predicted from their chemical structure.We have already found the formation of magnetic self-assemblies in nitronyl nitroxyl (4,4,5,5-tetramethyl-4,5-dihydro-1 H-imidazoline-1 oxyl-3-oxide) derivatives carrying heterocycles with the NH site, such as the imidazol-2-yl, benzimidazol-2-yl, naphth[2,3-d]imidazol-2-yl and azaindol-2-yl rings. Among these compounds, the benzimidazole derivatives formed a piled columnar assembly induced by intra- and intermolecular hydrogen bondings between an NH site and two nitroxyl O atoms. The assembly exhibited a 1D ferromagnetic chain behavior (J=ca.13〜16 cm^<-1>) that could be rationalized by through space close contact between the singly occupied molecular orbitals (SOMOs).To enhance the magnetic interaction in molecular systems, it is favorable to design multipoint close contacts between the SOMOs, because intermolecular magnetic interaction is described by the sum of the spin-density product of nearby atoms belonging to neighboring molecules. We also focused on 2,2-diphenyl-1,2-dihydroquinoline-1-oxyl and found several interesting magnetic characteristics in chemically modified derivatives.