Instituto de Ciencia de Materiales de Aragón, CSIC and Universidad de Zaragoza, Zaragoza, Spain.
J Phys Chem B. 2011 Mar 31;115(12):3003-12. doi: 10.1021/jp109489g. Epub 2011 Mar 7.
The relevance of abrupt magnetic and optical transitions exhibiting bistability in spin-crossover solids has been pointed out for their potential applications in optical or memory devices. In this respect, triazole-based one-dimensional coordination polymers are widely recognized as one of the most interesting systems. The measure of the interaction among spin-crossover centers at the origin of such cooperative behavior is of paramount importance and has so far been realized through modeling of spin-crossover curves derived mostly from magnetic measurements. Here, a new series of triazole-based one-dimensional coordination polymers of formula Fe(Rtrz)(3)(2)·xH(2)O with R = methoxyethyl and A = monovalent anion has been prepared that show complete and abrupt spin-crossover phenomenon as shown by magnetic measurements. The spin-crossover transition in these and related compounds is studied by differential scanning calorimetry, and the thermodynamic excess enthalpies and entropies associated with the phenomenon are derived systematically. Then the cooperative character of the spin-crossover in these materials is quantified by use of two widely used models, so-called Slichter and Drickamer and domain models. The same procedure is applied to spin-crossover curves of similar compounds available in the literature and for which calorimetric studies have been reported. The experimental thermodynamic figures, in particular the excess enthalpies, are shown to be clearly correlated to the output parameters of both models, thus providing a direct, experimental, quantitative measure of the cooperative character of the spin-crossover phenomenon.
具有磁和光双稳性的突跃磁转变在自旋交叉固体中的相关性，已被指出可用于光学或存储器件等潜在应用。在这方面，基于三唑的一维配位聚合物被广泛认为是最有趣的体系之一。引发这种协同行为的自旋交叉中心之间相互作用的度量非常重要，迄今为止，主要通过对主要来源于磁测量的自旋交叉曲线进行建模来实现。在此，我们合成了一系列新的基于三唑的一维配位聚合物Fe(Rtrz)(3)(2)·xH(2)O（其中 R = 甲氧基乙基，A = 单价阴离子），这些化合物通过磁测量表现出完全和突跃的自旋交叉现象。通过差示扫描量热法研究了这些化合物及相关化合物中的自旋交叉转变，系统地推导出与该现象相关的热力学过剩焓和熵。然后，使用两种广泛使用的模型，即所谓的 Slichter 和 Drickamer 模型和畴模型，对这些材料中的自旋交叉协同性进行了量化。该方法还应用于文献中可获得且已有量热研究报道的类似化合物的自旋交叉曲线。实验热力学数据，特别是过剩焓，与两个模型的输出参数明显相关，从而为自旋交叉现象的协同性质提供了直接、实验、定量的衡量。
