Coupled Crystallographic Order-Disorder and Spin State in a Bistable Molecule: Multiple Transition Dynamics
Coupled Crystallographic Order-Disorder and Spin State in a Bistable Molecule: Multiple Transition Dynamics
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DOI：
10.1002/chem.201003197
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发表时间：
2011-03-01
影响因子：
4.3
通讯作者：
Aromi, Guillem
中科院分区：
文献类型：
--
作者：
Craig, Gavin A.;Sanchez Costa, Jose;Aromi, Guillem
一种新的含有侧基苯酚的双吡唑基吡啶配体H4L，形成了一个具有复杂分子间相互作用网络的Fe-II自旋交叉(SCO)络合物[Fe(H4L)(2)]-[ClO4](2)中心点H2O中心点2(CH3)(2)CO(1)。由于自旋转变，它表现出40K宽的磁滞(T-0.5值为133K和173K)，并且具有不对称的非常丰富的结构。后者是上海合作组织与晶体相变耦合的结果。高自旋态也可能是热囚禁的，表现出非常大的T-TIESST(约104K)。在不同的温度下测定了1的结构，该晶体经过不同的过程来重建磁滞循环和热陷阱的关键点：200K，冷却到150K，在100K(高自旋，HS)下捕获，缓慢冷却到100K，升温到150K(低自旋，LS)。在HS状态下，体系的某些组分(一个ClO4-和两个丙酮分子)总是表现出无序状态，而LS相的Fe-N键长相对减少了9%，晶胞的各向异性收缩。最重要的是，在LS状态下，所有物种总是被发现是有序的。因此，本文首次从实验上证明了与SCO耦合的晶体有序无序的双稳态。文1中单胞参数的变化也表现出滞后。该化合物的结构和磁热变化与差示扫描量热法测量的热容变化是平行的。尝试用类伊辛模型来模拟1的不对称SCO行为，强调了动力学在SCO和晶体相变之间的耦合中的重要作用。
A novel bispyrazolylpyridine ligand incorporating lateral phenol groups, H4L, has led to an Fe-II spin-crossover (SCO) complex, [Fe(H4L)(2)]-[ClO4](2)center dot H2O center dot 2(CH3)(2)CO (1), with an intricate network of intermolecular interactions. It exhibits a 40 K wide hysteresis of magnetization as a result of the spin transition (with T-0.5 of 133 and 173 K) and features an unsymmetrical and very rich structure. The latter is a consequence of the coupling between the SCO and the crystallographic transformations. The high-spin state may also be thermally trapped, exhibiting a very large T-TIESST (approximate to 104 K). The structure of 1 has been determined at various temperatures after submitting the crystal to different processes to recreate the key points of the hysteresis cycle and thermal trapping; 200 K, cooled to 150 K and trapped at 100 K (high spin, HS), slowly cooled to 100 K and warmed to 150 K (low spin, LS). In the HS state, the system always exhibits disorder for some components (one ClO4- and two acetone molecules) whereas the LS phases show a relative approximate to 9% reduction in the Fe-N bond lengths and anisotropic contraction of the unit cell. Most importantly, in the LS state all the species are always found to be ordered. Therefore, the bistability of crystallographic order-disorder coupled to SCO is demonstrated here experimentally for the first time. The variation in the cell parameters in 1 also exhibits hysteresis. The structural and magnetic thermal variations in this compound are paralleled by changes in the heat capacity as measured by differential scanning calorimetry. Attempts to simulate the asymmetric SCO behaviour of 1 by using an Ising-like model underscore the paramount role of dynamics in the coupling between the SCO and the crystallographic transitions.