Magnetic Interaction Mechanism in Organic Magnetic Solids

自1991年第一个有机铁磁性化合物被发现以来，人们一直致力于通过合成各种氮氧自由基衍生物来实现晶相的铁磁性有序。然而，从微观角度看，铁磁有序化的机理还没有被阐明。在本研究项目中，我们从超精细耦合常数(HFCC)出发，研究了18种磁性化合物晶相中自由基分子每个原子上的电子自旋密度分布。根据固态高分辨魔角自旋^1H-，^2H-，^&lt；13&gt；C-和^&lt；19&gt；F-核磁共振谱的费米接触位移随温度的变化确定了hfcc。特别是高速魔角旋转的氘核磁共振方法对于研究分子间磁相互作用的局域磁结构和机理是非常有用的。调查的物种为氮氧化物、硝基硝基…更多的氧化物和亚胺氮氧化合物。用UBLYP和UB3LYP方法对一个孤立的分子、二聚体和Trimmer团簇模型进行了HFCC理论计算，并与实验结果进行了比较。该计划还扩展到氢键/电子/晶格耦合系统和磁性材料，包括磁性的铜(11)离子。(1)单占据分子轨道扩散到TEMPO导数的一个轴向甲基氢原子上，在氢原子上出现正电子自旋，而在另外两个氢原子上通过自旋极化机制诱导负自旋。因此，通过轴向甲基的磁性相互作用可以是铁磁性的，也可以是反铁磁性的，这取决于乙基的取向和相互作用的几何结构。(2)精确研究了6种不同氢键角的磁性固体通过氢键的磁性相互作用。通过氢键的磁性相互作用敏感地依赖于氢键角。强的铁磁相互作用是通过几乎90度键角的氢键来调节的。(3)磁相互作用路径中的杂原子孤对电子减弱了电子的自旋极化，铁磁相互作用变弱。(4)在pi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的变化的影响是一致的。较少

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