| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 1998: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1997: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
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
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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
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