The crystal engineering approach Towardmolecule-Basedmagneticmaterials by controlling the molecular arrangement of the stable radical based on the directionality of the hydrogen bonding is described in connection with the magnetic and orbital interactions between the radical units. Several derivatives of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl-3-oxide (NN) carrying a heterocycle having an NH proton donor site at the 2-position were designed. The imidazole derivative, Im-NN, formed a hydrogen-bonded chain, and close contact between the NO bonds of the NN group were observed between the chains. The benzimidazole and naphthoimidazole derivatives, BIm-NN and NIm-NN, formed a 1D assembled structure induced by intra- and intermolecular hydrogen bonds. Magnetic measurements revealed that a strong ferromagnetic interaction existed in BIm-NN, while dimeric and 1D chained antiferromagnetic interactions were observed in Im-NN and NIm-NN, respectively. The magneto-structural correlation of the 4- and 5-azaindole derivatives (4NIn-NN, 5NIn-NN) is also descried. In these crystals, the hydrogen bonds and -stacking have an important role in the crystal scaffolding, and the occurrence of a magnetic interaction is explained by contact of the SOMOs. These results indicate that the NHCC(NO)NO moiety is a useful synthon for propagating intermolecular magnetic interactions.
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