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Polymorphism and Magnetism of Organic Radical Crystals

有机自由基晶体的多晶型和磁性

基本信息

批准号：
07640767
负责人：
KINOSHITA Minoru
金额：
$ 1.28万
依托单位：
Science University of Tokyo in Yamaguchi
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640767/
关键词：
Organic ferromagnet Ferromagnetic interactoin Phase transition Polymorphism Galvinoxyl p-NPNN Hydrogen bond Crystal structure

项目摘要

Organic radicals of galvinoxyl and p-nitrophenyl nitronyl nitroxide (p-NPNN) playd crucial roles in the discovery of purly organic ferromagnet. These two and some related compounds exhibit polymorphism and variety of magnetism. This was quite important in elucidating the mechanism of magnetic interactions, because the polymorphic forms are closely related to one another in crystal structure. Galvinoxyl exhibits ferromagnetic interaction in the high temperature phase, but it is non-magnetic below 85K.The crystal structure is known for the high temperature phase, but it is unknown at low temperature. In this project, we have tried to determine the crystal structure of its low temperature phase. We could obtain the x-ray diffraction pattern at about 10K.However, the crystal became twinned and extra spots appeared prevented us from final analysis of the pattern. We then tried to find a way to cool the crystals without crushing at the phase transtion temperature. Various ways could not succeed. During the course of testing various ways, however, we could succeed in finding the way to surpress the phase transition by applying pressure and to maintain the ferromagnetic interaction down to low temperature. As for the phase transitions in p-NPNN,model calculation indicates an importance of librational motion of the molecules in exhibiting the polymorphism.

高维氧基和对硝基苯基硝基氮氧化物（p-NPNN）的有机自由基在纯有机铁磁体的发现中起着至关重要的作用。这两种化合物及其相关化合物表现出多态和磁性的多样性。这对于阐明磁相互作用的机制是非常重要的，因为多晶形式在晶体结构上彼此密切相关。Galvinoxyl在高温阶段表现出铁磁相互作用，但在85K以下表现为非磁性。高温相的晶体结构是已知的，但低温相的晶体结构是未知的。在这个项目中，我们试图确定其低温相的晶体结构。我们可以在10K左右得到x射线衍射图。然而，晶体变成了孪生，并且出现了额外的斑点，使我们无法对图案进行最终分析。然后，我们试图找到一种方法来冷却晶体，而不会在相变温度下破碎。各种方法都无法成功。然而，在测试各种方法的过程中，我们成功地找到了通过施加压力来抑制相变并将铁磁相互作用保持在低温下的方法。对于p-NPNN中的相变，模型计算表明分子的振动运动在表现多态性方面很重要。