Synthesis and Magnetic Properties of Nitronyl Nitroxides with an Adjacent Chiral Group

We have designed and synthesized chiral molecules with nitronyl nitroxide (NN) radicals directly bound to the chiral centers, (S)-1,3-dioxolane-4-NN (1) and (R)-oxazolidine-4-NN (2). These radicals were synthesized from D-mannitol in four steps for 1 and from L-serine in six steps for 2 in moderate yields. They were characterized by means of mass spectrometry, electron spin resonance, elemental analyses, and X-ray crystal structure analyses. Their magnetic properties were also investigated using a SQUID magnetometer. The temperature dependence of paramagnetic susceptibility (chi(p)) indicates the presence of a weak antiferromagnetic intermolecular interaction with J/k(B) = -3.1 K and theta = -5.5 K for 1, and a weak ferromagnetic intermolecular interaction with J/k(B) = +0.5K for 2. We also succeeded in preparing the metal complex [Mn(hfac)(2)(2)](2)-[Cu(hfac)(2)], which was characterized by a strong antiferromagnetic interaction (J/k(B) = -140 K) between [Mn(hfac)(2)] and 2 along with a much weaker antiferromagnetic interaction (J/k(B) = -0.11 K) between the [Mn(hfac)(2)(2)] unit and [Cu(hfac)(2)].