Katsuya INOUE and Hiizu IWAMURA (Kyushu Univ.)
[Proc. Mater. Res. Soc. 413, 313 (1996)]
A strategy of assembling and aligning spins of organic free radicals by means of complexation with magnetic metal ions has been pursued for obtaining ferro/ferrimagnets with high phase-transition temperature (TC). Triplet m-phenylenebis(t-butylnitroxide) and 2,4-bis(4,4,5,5-tetramethyl-4,5-dihydro-1-oxido-3-oxyimidazol-2-yl)thiophene formed with d5 bis(hexafluoro-acetylacetonato)manganese(II) {Mn(hfac)2} a 1D chain and a ladder-type polymer that proved to be a metamagnet (5.5 K) and a ferro/ferrimagnet (11 K), respectively. Quartet 1,3,5-tris{p-(N-oxy-tert-butylamino)phenyl}benzene and the lower analogs formed with {Mn(hfac)2} 2D network structures with TC in the range 3.4-9.3 K. Bis-{3-tert-butyl-5-(N-oxy-tert-butylamino)phenyl} nitroxide with a quartet ground state formed a 2:3 complex with Mn(hfac)2. The terminal two nitroxide groups of the trinitroxide radicals are ligated to two different Mn ions to form a zigzag chain. The middle nitroxide group is used to cross-link the adjacent chains through a third Mn ion, resulting in the formation of a parallel-crosses-shaped 3D structure. The temperature dependence of the magnetization at 5 Oe revealed a transition to the spin-ordered phase at 46 K. Efforts are in progress to make organic polyradical/magnetic ion hybrid-spin systems with higher TC and endow the magnetic materials with photo-responsiveness and other functionality.