A new stable organic radical, 2,3,6-trifluorophenyl nitronyl nitroxide (=2-(2,3,6-trifluorophenyl)-4,4,5,5- tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide) was synthesized, and its crystal structure and magnetic properties were examined. The magnetization curve measured at 0.4K in magnetic field up to 30 T revealed two-step saturation. A magnetization plateau was observed when the magnetization was one half the value of the saturation magnetization. The temperature dependence of the product of paramagnetic susceptibility (X p) and temperature (T), XpT (XpT æ μeff 2, square of the effective magnetic moment) showed stationary behavior in the range 24K at two-thirds the value at room temperature. The magnetic structure of this material could be elucidated on the basis of magnetization (M) measurements. Complementary analysis of X pT and M revealed the formation of magnetic clusters comprising triplet (S = 1) and singlet (S = 0) species in the ground state. The intradimer interactions were attributed to the special molecular overlaps, as reported previously. Interdimer interactions were also investigated: the difference in the molecular overlap between the trifluorophenyl groups was responsible for the difference in the sign of the magnetic coupling. This is the first experimental evidence for the molecular overlap between the phenyl groups being responsible for the strong magnetic interactions.
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