Construction of Organic Magnetic Metals and Magnetic Composits using Spin-Polarized Donors

为了构建磁性有机-无机纳米复合材料，合成了交叉共轭和超共轭自旋极化的给体分子及其吸附的金纳米颗粒。在四辛基溴化铵存在下，HAuCl4还原合成了约4 nm的金纳米颗粒，通过化学吸附制备了几种由金纳米颗粒组成的纳米复合材料。得到的固体样品呈现单线ESR信号，谱线宽度在1.5~30mT之间。其中，由自旋极化施主类型的硝基氮氧化物功能化的纳米颗粒表现出非常广泛的信号。该自由基的分子轨道计算表明，硫原子在金表面的吸附位置有较大的自旋极化。当加入抗磁性配体后，纳米颗粒表面的自旋极化施主自由基浓度降低，线宽变小。这些结果表明，虽然ESR信号的线宽一般与基团局域自旋之间的自旋-自旋弛豫有关，但考虑到金纳米颗粒导电电子的辅助作用，ESR信号的线宽是合理的。虽然纳米复合样品中存在传导电子与局域自旋的相互作用，但通过磁化率测量发现，金纳米颗粒上自由基间的磁相互作用是顺磁性的。构建磁性纳米复合材料的研究正在进行中。

The research project was carried out syntheses of the cross-conjugated and hyper-conjugated spin-polarized donor molecules and preparation of their adsorbed gold nanoparticles in order to construct the magnetic organic-inorganic nano-composites.Several Nano-composites consisted of gold nanoparticle were prepared by the chemical adsorption of some nitroxide radicals on the surface of ca. 4 nm gold nanoparticles which were synthesized by reduction of HAuCl_4 at the presence of tetraocyl ammonium bromide. The obtained solid samples of the nanoparticles showed singlet ESR signals that the line widths were within 1.5 〜 30 mT. Among them, the nanoparticles functionallized by the spin polarized donor typed nitronyl nitroxide exhibits extraordinarily broad signal. Molecular orbital calculation of this radical indicated a large spin polarization at the site of sulfur atom that is the attaching site to the gold surface. As the concentration of the spin polarized donor radical on the surface of nanoparticles was reducing by mixing a diamagnetic ligand, the line width became small. These results indicated that the line broadening of ESR signal rationalized by considering of the assistant of the conduction electrons of gold nanoparticle for the spin relaxation, although the line width of ESR signals generally correlates with the spin-spin relaxation among the localized spins of radicals.While the interaction of the conduction electrons with localized spins was recognized for the nano-composite samples, it was found by the measurement of magnetic susceptibility that the magnetic interaction between radicals on gold nanoparticles was paramagnetic. The researches for the construction of the magnetic nano-composite are in progress.