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Magnetic Interaction Mechanism in Organic Magnetic Solids

有机磁性固体中的磁相互作用机制

基本信息

批准号：
09640681
负责人：
TAKEDA Sadamu
金额：
$ 2.05万
依托单位：
GUNMA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640681/
关键词：
Magneric Local Structure Magnetic Inetraction Organic Ferromagnetic Compounds Electron Spin Density Hydrogen Bonds Magic Angle Spinning Deuterium NMR Molecular Orbital Calculation Solid-State High-Resolution NMR 有機磁性結晶固体高分解能重水素核NMR 高速

项目摘要

Since the first organic ferromagnetic compound was found in 1991, considerable effort has been made to realize ferromagnetic ordering in the crystalline phase through the synthesis of a variety of derivatives of the nitroxide radical species. However, the mechanism of ferromagnetic ordering has not yet been clarified in a microscopic view point. In this research project, we studied electron spin density distribution on each atom of radical molecules for 18 species of magnetic compounds in their crystalline phases from hyperfine coupling constants (hfcc). The hfccs were determined from the temperature dependence of the Fermi contact shifts of solid-state high-resolution magic angle spinning ^1H-, ^2H-, ^<13>C-, and ^<19>F-NMR spectra. Particularly high-speed magic angle spinning deuterium NMR method was confirmed to be very useful for the investigation of local magnetic structure and mechanism of intermolecular magnetic interac- tion. The investigated species are nitroxides, nitronylnit … More roxides, and iminonitroxides. Theoretical calculations of hfcc based on UBLYP and UB3LYP were also performed for an isolated molecule, dimer, and trimmer cluster models to compare the calculations with the experimental results.The following points were concluded to be important for controlling the magnetic interaction in the organic magnetic crystals. The project was also extended to hydrogen-bond/electron/lattice coupling systems and to magnetic materials including magnetic Cu(ll) ion.(1) Single occupied molecular orbital spreads to one of the axial methyl hydrogen atoms of TEMPO derivatives and positive electron spin appears on the hydrogen atom, whereas negative spin is induced on the other two hydrogen atoms by spin polarization mechanism. Thus the magnetic interaction through the axial methyl group can be ferromagnetic and antiferromagneric one depending on the orientation of the ethyl group and on the interaction geometry.(2) The magnetic interaction through hydrogen bonds was precisely investigated for 6 magnetic solids with different hydrogen bond angle. The magnetic interaction via hydrogen bond sensitively depends on the hydrogen bond angle. Strong ferromagnetic interaction is mediated through the hydrogen bond with almost 90 degree of the bond angle.(3) Lone-pair of electrons of hetero-atom included in the magnetic interaction path diminishes the electron spin polar- ization and ferromagnetic interaction becomes weak.(4) An effect of introduction of hetero-atoms in pi-conjugated system on the spin polarization mechanism is compamble to the effect of a change of molecular geometry. Less

自1991年发现第一个有机铁磁化合物以来，人们通过合成各种氮氧化物自由基衍生物来实现结晶相的铁磁有序。然而，铁磁有序的机理尚未从微观角度阐明。本课题从超精细耦合常数（hfcc）的角度研究了18种磁性化合物在其晶相中原子团原子上的电子自旋密度分布。hfccs是根据固态高分辨率魔角旋转^1H-， ^2H-, ^<13>C-和^<19>F-NMR光谱的费米接触位移的温度依赖性来确定的。特别是高速魔角自旋氘核磁共振法在研究分子间磁相互作用机理和局部磁结构方面具有重要的应用价值。所研究的种类有氮氧化物、亚硝基氮氧化物和亚硝基氮氧化物。基于UBLYP和UB3LYP对分离分子模型、二聚体模型和聚簇模型进行了理论计算，并与实验结果进行了比较。总结出以下几点对于控制有机磁性晶体中的磁相互作用是重要的。该项目还扩展到氢键/电子/晶格耦合系统和磁性材料，包括磁性Cu（ll）离子。(1) TEMPO衍生物的单占据分子轨道向其中一个轴向甲基氢原子扩散，氢原子上出现正电子自旋，而另外两个氢原子则通过自旋极化机制诱导负电子自旋。因此，通过轴向甲基的磁相互作用可以是铁磁性的和反铁磁性的，这取决于乙基的取向和相互作用的几何形状。(2)对6种不同氢键角的磁性固体进行了氢键磁相互作用的精确研究。通过氢键的磁相互作用敏感地依赖于氢键角。强铁磁相互作用通过氢键介导，键角约为90度。(3)异质原子的单对电子加入磁相互作用路径，使电子自旋极化减弱，铁磁相互作用减弱。(4) π共轭体系中引入杂原子对自旋极化机制的影响与分子几何结构变化的影响相当。少