A low-dimensional molecular spin system with two steps of magnetic transitions and liquid crystal property
A low-dimensional molecular spin system with two steps of magnetic transitions and liquid crystal property
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具有两步磁跃迁和液晶性质的低维分子自旋系统
DOI：
10.1039/c0dt01704c
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发表时间：
2011-01-01
影响因子：
4
通讯作者：
Zhou, Shi-Ming
中科院分区：
文献类型：
--
作者：
Duan, Hai-Bao;Ren, Xiao-Ming;Zhou, Shi-Ming
设计并合成了一种低维化合物[C-6-Apy][Ni（mnt）（2）]（1，其中mnt（2-）=马来腈二硫醇盐，C-6-Apy（+）= 4-氨基-1-己基吡啶），该化合物具有阴、阳离子的层状排列，并显示出两步磁跃迁。低温磁转变具有不寻常的磁滞回线，而晶体结构研究揭示了没有结构转变的磁转变。高温磁转变具有两个显著的特点：（1）在第一次加热过程中，它与晶体-中间相转变同步发生;（2）伴随固体-中间相转变的结构变化是不可逆的。通过结构、DSC和POM技术对一个抗磁性的同构化合物[C-6-Apy][Cu（mnt）（2）]进行了表征，发现在[C-6-Apy][Ni（mnt）（2）]的相同温度区间内存在不可逆的晶相-中间相转变。因此，1中的高温磁转变是由结构应变的释放驱动的，而不是磁弹性相互作用。该中间相具有近晶A相的特征，阳离子层中的烷基链熔融可能导致中间相的形成。值得注意的是，在己基烃链分子体系中发现中间相与建议的至少需要十二烷基链的规则相反。我们的研究结果将有助于设计和制备一种新的低维分子系统结合磁性转变和液晶性能。
A low-dimensional compound [C-6-Apy][Ni(mnt)(2)] (1, where mnt(2-)=maleonitriledithiolate, C-6-Apy(+) = 4-amino-1-hexylpyridinium) has been designed and synthesized, which has layer arrangement of anions and cations and shows two steps of magnetic transitions. The low temperature magnetic transition has an uncommon hysteresis loop, while the crystal structure investigations disclosed no structural transition with the magnetic transition. The high temperature magnetic transition exhibits two remarkable features: (1) it synchronously occurs with a crystalline-to-mesophase transition in the first heating process and (2) the structural changes that accompany the solid-mesophase transition are irreversible. A diamagnetic and isostructural compound, [C-6-Apy][Cu(mnt)(2)], is further characterized by structure, DSC and POM techniques, which revealed also the existence of an irreversible crystalline-to-mesophase transition in the same temperature interval of [C-6-Apy][Ni(mnt)(2)]. Therefore, the high-temperature magnetic transition in 1 is driven by release of the structural strains, but not magnetoelastic interactions. The mesophase exhibits the characteristic of smectic A phase, and the alkyl chain melting in the cation layers probably lead to the formation of mesophase. It is noticeable that the finding of a mesophase occurring in a hexyl hydrocarbon chain molecular system is in contrast to a suggested rule that at least a dodecyl chain is required. Our results will shed a light on the design and preparation of a new low-dimensional molecular system combining magnetic transition and liquid crystal properties.