1998 Volume 71 Issue 11 Pages 2583-2587
Temperature dependences of d.c. magnetic susceptibilities and magnetizations were measured for two different crystallographic phases of 4-(4-iodobenzylideneamino)-2,2,6,6-tetramethylpiperidin-1-yloxyl. Intermolecular ferromagnetic (Weiss temperature θ = +0.71 K) and antiferromagnetic (θ = −0.23 K) interactions were found for α- and β-phases, respectively, in the magnetic measurements above 1.8 K; the former phase showed a bulk ferromagnetic transition at 0.28 K. Based on the X-ray crystallographic data, intermolecular magnetic interactions are discussed. In the α-phase crystal, NO-radical sites form two-dimensional zigzag sheets. The ferromagnetic interaction within the sheet can be interpreted in terms of a β-hydrogen mechanism, ON(↑)–Cα(↓)–Cβ(↑)–Hβ(↓)···(↑)ON<, in which the magnetic interaction is transmitted by β-hydrogens. A dimer structure was found in the β-phase crystal, and direct exchange and/or dipole interactions between N–O radicals seem to be the main origin of the antiferromagnetic interaction.
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