同位素取代调控一维spin-Peierls-type分子磁体磁相变性质研究

Spin transition/spin bistability compounds are the new type of technically-important functional material, which possess the potential applications in the technical areas, such as, thermal switch, optical switch and information storage. In this project, we will develop a strategy for tuning the magnetic and phase transition features of the one-dimensional spin-Peierls-type compounds, which are based on metal-bis-dithiolene building blocks, via isotope substitution. In our previous studies, a series of organic cations with flexible molecular conformation were designed and combined with the magnetic metal-bis-dithiolene anions to give one-dimensional molecule-based magnets, and those molecule magnets showed one or two steps of spin-Peierls-type transition at a certain temperature, which are promoted by the strong spin-lattice coupling interactions. Theoretically, the spin-Peierls-type transition and magnetic feature of one-dimensional metal-bis-dithiolene compounds are probably varied with the isotope substitutions for the components of the compound since the lattice vibration feature and the zero-point energy are related to the molecule mass. The components of spin-Peierls-type compounds, based on metal-bis-dithiolene building blocks, will sequentially be isotopely substituted and the corresponding substitued compounds are comparelly investigated in the aspects of vibration spectroscopies, crystal structures, magnetic, phase transition and thermodynamic properties. Based on the calculation using the First-principles electronic band structure theory for the one-dimensional spin-Peierls-type molecule magnets, the density of states near the Fermi level will be further analyzed, which be expected to reveal the issues, for instance, the intrinsic mechanism of the isotope effect on the spin-Peierls-type transition,the crucial lattice vibration models as well as other factors that affect strongly on the spin-Peierls-type transition feature. The correlation of isotope substitution and spin-Peierls-type transtion feature will be built and the approach for tuning the spin transition property via isotope substitution will be developed as well. This study will be aim to provide the useful information for the desination and contrallable preparation of new spin transition functional compounds whose properties, such as the critical temperature and the hysteretic loop width, are hoped to meet the technical requirements.

自旋转换/自旋双稳性化合物是新型机敏材料，在未来分子热开关、光开关和信息存储等高技术领域具有重要应用前景。本项目拟开展'同位素取代调控一维spin-Peierls-type分子磁体磁相变性质'方面研究工作。通过对我们前期发现的一系列一维过渡金属二硫烯spin-Peierls-type自旋转换/自旋双稳性化合物中各组分逐步同位素取代，比较研究其单晶结构、磁、相变热力学、晶格振动等性质。用第一性原理计算一维晶体能带结构、分析Fermi能级附近态密度，揭示spin-Peierls-type磁相变同位素效应内在机制、协同spin-Peierls-type磁相变的关键晶格振动模、以及影响spin-Peierls-type磁相变性质关键因素。在实验和理论基础上，建立同位素取代-磁相变性质之间相关性，发展同位素取代调控磁相变性质的方法。为设计、定向合成关键技术参数满足实用要求的磁相变化合物提供理论依据。

自旋转换/自旋双稳性化合物是新型机敏材料，在分子热开关、光开关和信息存储等高技术领域具有重要应用前景。在此本项目研究中，我们合成了6个含不同取代基的苄基吡啶阳离子[R-Bz-Py]（R = F、I、NO2、CH3、CN、CH=CH2）与-1价[Ni(mnt)2]构筑的一维spin-Peierls-type分子磁体，5个含-1价[Pt(mnt)2]的一维spin-Peierls-type分子磁体。通过用氘代吡啶取代苄基吡啶阳离子中吡啶结构单元，我们分别制备和表征了6个含-1价[Ni(mnt)2]、5个含-1价[Pt(mnt)2]的同位素取代类似物。比较研究了阳离子中含吡啶结构单元和含氘代吡啶结构单元化合物的晶体结构、变温红外光谱、磁化率和DSC等性质。与苄基吡啶盐相比，氘代苄基吡啶的[Ni(mnt)2]化合物中4个盐的磁相变温度分别升高2-8 K，一个盐磁相变温度降低3 K，一个盐磁相变消失；而5个氘代苄基吡啶的[Pt(mnt)2]化合物的磁相变温度几乎与其苄基吡啶[Pt(mnt)2]化合物相同。通过对[Br-Bz-Py][Ni(mnt)2]中苄基（Bz）和吡啶（Py）结构单元中氢原子逐步用氘原子取代，我们比较研究4个相关化合物的单晶结构、磁、相变、晶格振动等性质，结果表明，吡啶环上氢原子氘代导致的同位素效应比苄基（Bz）上氢原子氘代同位素效应显著，其原因可能与阴离子CN与吡啶环上氢原子之间氢键作用有关。[Ni(mnt)2]和[Pt(mnt)2]系列具有显著不同的同位素效应，揭示两个系列同位素效应的机制可能不同。进一步通过设计合成新的柔性构象有机阳离子，并分别与金属二硫烯分子构筑块[Ni(mnt)2]、[Ni(dmit)2和[Ni(dmit)(mnt)]组装，我们制备和表征了新的一维电荷转移盐系列，发现了新的spin-Peierls-type系列化合物。新系列磁相变化合物表现出磁、介电可开关性质，热退火诱导磁、介电可开关性质，光诱导电导增强性质等新奇功能性质。新系列多功能spin-Peierls-type磁体的同位素取代研究（包括制备、结构、磁、电导、介电以及DSC（比热），以及晶体电子带结构计算等）都正在有序开展之中。本项目的研究结果为进一步合理设计、定向构筑关键技术参数满足实际应用要求的磁相变化合物，深刻理解磁相变以及同位素效应机制提供理论依据。