CRYSTAL STRUCTURES OF TEMPO RADICALS SHOWING FERROMAGNETIC INTERACTIONS. H. Yamamoto, H. Yoshikawa, M. Yasui, T. Ishida, T. Nogami and F. Iwasaki, Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182, Japan

Some of the 4-arylmethyleneamino-TEMPO radicals (TEMPO = 2,2,6,6-tetramethyl-piperidin-1-oxyl) were revealed to show inter-molecular ferromagnetic interactions, of which 1 _~ 5 and 13 exhibit a ferromagnetic transition (Tc) at an extremely low temperature [T. Nogami, et al. Chem. Letters, 29-32 (1994), T. Ishida et al. Chem. Letters, 919-922 (1994)]. 6 ~ 11 showed only a ferromagnetic interaction ([[theta]] > 0), while 12 showed an antiferromagnetic interaction ([[theta]] < 0). The X-ray structure analyses were performed on these crystals at room temperature to investigate whether any systematic intermolecular interactions were demonstrated among these crystals.

Ar-CH=N-TEMPO* (Ar: 1 Ph; 2 p-Cl-Ph; 3 p-biPh; 4 p-PhO-Ph; 5 p-PhS-Ph; 6 p-Br-Ph; 7 3,5-diCl-Ph; 8 2-Py; 9 3-Py; 10 4-Py; 11 Naph; 12 p-F-Ph) Ar-CH2NH-TEMPO* (Ar: 13 Ph)

For all crystals, two-dimensional O^...O networks are constructed, although of which forms are various. In 2, O atoms arrange to form a pleated sheet with the first and the second nearest O^...O distances of 5.91 and 5.96 Å, respectively. Between sheets the aryl groups of each sheet arrange alternately with face-to-face. Crystal structures of 3, 6 and 10 belong to the same category as 2. In 1 and 9, which are isomorphous, top and bottom lines of the pleats are not straight but zigzag. The nearest aryl groups belonging to the neighboring sheets arrange herringbone-like. The networks of 7 and 12 are constructed with zigzag lines, so that the surface of the sheet is rough in all directions. In 4, there are no intersheet interactions between aryl groups, because the sheet is almost flat perpendicular to the crystallographic polar axis. This arrangement is quite different from the other crystals. In all these crystals sheet-like arrangement of the N-O radicals are considered to be essentially important for the magnetic interactions. Magnetic interactions may be transferred via intermolecular interactions of side chains, since the intra- and intersheet O^...O distances are so long for the direct evidence of the systematic interactions which manifests the magnetic character.