DEVELOPMENT OF MOLECULE-BASED FERROMAGNETS UTILIZING STABLE ORGANIC RADICALS OR PYRIMIDINE-TRANSITION METAL COMPLEXES

(1)有机自由基的磁性研究用SQUID方法研究了165种TEMPO衍生物(Arc=N-TEMPO，Ar=芳基)的磁性，发现52个自由基具有分子间铁磁相互作用。因此，分子间的铁磁相互作用并不少见。在0.4K以下，8种自由基发生了体相变，我们认为这种铁磁相互作用是通过β-氢的自旋极化机制引起的。这一机理得到了MO计算和核磁共振测量的支持。通过零场MuSR测量，在T_c以下观察到自发磁化强度。为了提高体系的转变温度，研究了pi-共轭NO自由基的磁性。(2)嘧啶过渡金属络合物的磁性为了研究过渡金属离子与芳环间位配位的磁性，研究了不同类型的嘧啶过渡金属络合物的磁性。研究发现，决定磁相互作用的是配位方式而不是配位位置(间位)。在Cu^&lt；2+&gt；的情况下，轴/赤道配位引起铁磁相互作用，赤道/赤道配位引起反铁磁相互作用。当我们采用小尺寸的无机阴离子时，几种络合物表现出较弱的铁磁性。(嘧啶)_2CoX_2(X=Cl，Br)具有手性晶体结构，表现出较弱的铁磁性。

(1) Magnetic Properties of Organic RadicalsMagnetic properties of 165 kinds of TEMPO derivatives (ArCH=N-TEMPO,Ar=aryl group) were studied by SQUID Intermolecular ferromagnetic interactions were found for 52 radicals. Thus, the intermolecular ferromagnetic interaction were found to be not a rare phenomenon. Eight kinds of radicals showed bulk ferromagnetic transitions below 0.4 K.We proposed that the ferromagnetic interaction was caused by the spin-polarization mechanism via beta-hydrogens. This mechanism was supported by MO calculations and NMR measurements. Spontaneous magnetization was observed below T_c by means of zero-field muSR measurements. In order to elevate the transition temperatures, magnetic properties of pi-conjugated NO radicals were studied. NO radicals possessing acridine skeleton showed the intermolecular ferromagnetic interaction which was caused through the overlaps of pi-electron clouds (McConell model).(2) Magnetic Properties of Pyrimidine-Transition Metal ComplexesIn order to study the magnetic interactions of transition-metal ions coordinated to meta-positions of an aromatic ring, magnetic properties of various pyrimidine-transition metal complexes were studied. It was found that coordination modes rather than coordination positions (meta-position) determine the magnetic interactions. In the case of Cu^<2+> an axial/equatorial coordination gave rise to the ferromagnetic interaction, and an equatorial/equatorial coordination did the antiferromagnetic interaction. When we adopted inorganic anions of small sizes, sevral complexes showed the behavior of a weak ferromagnetism. (pyrimidine)_2CoX_2 (X=Cl, Br) has a chiral crystal structure, and showed the behavior of the weak ferromagnetism.