Maekawa Kensuke, Shiomi Daisuke, Ise Tomoaki, Sato Kazunobu, Takui Takeji
Department of Materials Science and Chemistry, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan.
J Phys Chem B. 2005 Mar 3;109(8):3303-9. doi: 10.1021/jp046092m.
As a novel molecular designing for genuinely organic molecule-based ferrimagnets, we have proposed a strategy of "single-component ferrimagnetics". When a pi-biradical with an S = 1 ground state and a pi-monoradical with S = (1)/(2) are united by sigma-bonds, the pi-conjugation between the biradical and the monoradical moieties should be truncated in the resultant triradical. This gives magnetic degrees of freedom for both S = 1 and (1)/(2) in the single molecule, serving as a building block for organic molecule-based ferrimagnets under favorable conditions (single-component ferrimagnetics). We have designed and synthesized a triradical, 3-(1'-oxyl-3'-oxido-4',4',5',5'-tetramethylimidazolin-2-yl)benzoic acid 2,4-bis(1' '-oxyl-3' '-oxido-4' ',4' ',5' ',5' '-tetramethylimidazolin-2-yl)phenyl ester (4), as a model compound for the novel approach to genuinely organic ferrimagnets. In the triradical 4, a m-phenylene-bis(nitronyl nitroxide) biradical with a triplet (S = 1) ground state is united with a phenyl nitronyl nitroxide monoradical (S = (1)/(2)) by an ester coupler. Solution-phase ESR spectra from 4 exhibited a complex hyperfine splitting due to (14)N and (1)H nuclei. The analysis of the hyperfine structure based on perturbation calculations has revealed that the exchange interaction within the biradical moiety is much larger than those between the biradical and the monoradical moieties and the magnetic degrees of freedom for both S = 1 and (1)/(2) are retained in 4. An X-ray crystal structure analysis showed that the triradical molecules are arranged in a one-dimensional molecular chain in the crystal. The magnetic susceptibility in a crystalline solid state is consistent with the crystal structure.
作为一种针对真正基于有机分子的铁磁体的新型分子设计，我们提出了“单组分铁磁体”策略。当具有S = 1基态的π-双自由基和具有S = 1/2的π-单自由基通过σ键结合时，双自由基和单自由基部分之间的π共轭在所得三自由基中应被截断。这为单分子中的S = 1和1/2都提供了磁自由度，在有利条件下（单组分铁磁体）可作为基于有机分子的铁磁体的构建单元。我们设计并合成了一种三自由基，3-(1'-氧基-3'-氧化-4',4',5',5'-四甲基咪唑啉-2-基)苯甲酸2,4-双(1''-氧基-3''-氧化-4'',4'',5'',5''-四甲基咪唑啉-2-基)苯基酯(4)，作为一种新型真正有机铁磁体方法的模型化合物。在三自由基4中，具有三重态(S = 1)基态的间亚苯基-双(硝酰基氮氧化物)双自由基通过酯连接体与苯基硝酰基氮氧化物单自由基(S = 1/2)结合。来自4的溶液相电子顺磁共振光谱由于(14)N和(1)H核表现出复杂的超精细分裂。基于微扰计算对超精细结构的分析表明，双自由基部分内的交换相互作用远大于双自由基和单自由基部分之间的交换相互作用，并且S = 1和1/2的磁自由度在4中得以保留。X射线晶体结构分析表明，三自由基分子在晶体中排列成一维分子链。晶体固态下的磁化率与晶体结构一致。
