Magnetic properties of organic free-radicals and charge-transfer complexes at low temperatures

有机自由基和电荷转移络合物在低温下的磁性

基本信息

批准号：
02453012
负责人：
SORAI Michio
金额：
$ 4.61万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

Magnetic properties of substances have been interpreted on the basis of either of two models : one is the itinerant-electron model for delocalized-electron systems and the other is the Heisenberg model for localized-electron systems. Organic free-radicals and charge-transfer complexes, in which the unpaired electron is not localized on a particular atom but delocalized over many atoms in a molecule to a great extent, belong to an intermediate category between the two models. Magnetic properties of these radicals have so far been described as a perturbation from the two extreme models. Main purpose of the present research project was to elucidate magnetic properties of organic free-radicals and charge-transfer complexes on the basis of precise heat capacity and magnetic susceptibility measurements at low temperatures.Compounds for which heat capacity measurements were made by adiabatic calorimeters involve (1) charge-transfer molecular ferromagnets, decamethylferrocenium-TCNE and decame … More thylferrocenium-TCNQ, (2) pure organic free-radicals, MOTMP and AOTMP, (3) charge-transfer complex TTF-CA that shows the ionicneutral phase transition, (4) binuclear mixed-valence complex, diiodobiferrocenium triiodide, and (5) mixed-metal coordination compounds, MnCu (obbz) H_2O, MnCu (obbz) 5H_2O, and NBu_4[CuCr (Ox) _3].All the magnetic compounds exhibited a phase transition peak arising from magnetic ordering and a heat capacity anomaly due to the short-range order effect. By applying the spin-wave theory to temperature dependence of the magnetic heat capacities at low temperatures, the dimensionality of the spin-lattice and the nature of the ordered spin state were determined. The spin-spin interaction in the radical complexes has been proved to be described by the Heisenberg model, in which only the exchange integral parameter is effectively modified. Observation of a Schottky anomaly in the mixed-valence complex, 1', l"'-diiodobiferrocenium triiodide, predicts that the intramolecular electron transfer occurs by a tunnel-mechanism. Less

物质的磁性可以基于两种模型之一进行解释：一种是离域电子系统的巡回电子模型，另一种是有机自由基和电荷转移络合物的海森堡模型。，其中不成对电子不局域于特定原子上，而是在很大程度上离域于分子中的许多原子上，属于这两个模型之间的中间类别。到目前为止，这被描述为两个极端模型的扰动，本研究项目的主要目的是在低温下精确的热容和磁化率测量的基础上阐明有机自由基和电荷转移络合物的磁性。通过绝热热量计进行热容量测量的化合物包括 (1) 电荷转移分子铁磁体、十甲基二茂铁-TCNE 和十卡姆……更多乙基二茂铁-TCNQ，(2) 纯有机自由基，MOTMP 和 AOTMP，(3) 显示离子中性相变的电荷转移络合物 TTF-CA，(4) 双核混合价络合物，二碘二茂铁三碘化物，以及 (5)混合金属配位化合物、MnCu(obbz)H_2O、MnCu(obbz)5H_2O和NBu_4[CuCr(Ox)_3]。通过将自旋波理论应用于磁热的温度依赖性，所有磁性化合物都表现出由磁有序引起的相变峰和由于短程有序效应而产生的热容量异常。低温下的容量、自旋晶格的维数和有序自旋态的性质已被证明可以用海森堡模型来描述，其中只有交换积分参数。对混合价络合物 1',l"'-二碘二铁铪三碘化物中肖特基异常的观察预测，分子内电子转移是通过隧道机制发生的。