Structural approach of the features of the spin crossover transition in iron(II) compounds
Structural approach of the features of the spin crossover transition in iron(II) compounds
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DOI：
10.1039/a808075e
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发表时间：
1999-04-01
影响因子：
--
通讯作者：
Kahn, O
中科院分区：
文献类型：
--
作者：
Guionneau, P;Létard, JF;Kahn, O
我们测定了四种Fe(PM-L)(2)(NCS)(2)配合物在高自旋态和低自旋态下的晶体结构，其中PM为N-2′-吡啶基亚甲基，芳香亚基L为4-氨基苯（TeA）、4-（苯偶氮）苯胺（AzA）、4-氨基联苯（BiA）或4-（苯乙基）苯胺（PEA）。如前所述，这些化合物在低温下进行自旋交叉，其转变具有不同的特征：Fe(PM-TeA)(2)(NCS)(2)非常光滑且不完全，Fe(PM-AzA)(2)(NCS)(2)平滑且几乎没有迟滞，Fe(PMBiA)(2)(NCS)(2)异常突然，Fe(PM-PEA)(2)(NCS)(2)具有非常大的迟滞（37 K）。在Fe(PM-BiA)(2)(NCS)(2)、Fe(PM-TeA)(2)(NCS)(2)和Fe(PM-AzA)(2)(NCS)(2)中，自旋转换与大的结构相变无关，在相变温度上下空间群相同：第一个为正交Peen，第三个为单斜P2(1)/c。另一方面，Fe(PM-PEA)(2)(NCS)（2)经历了从P2(1)/c大腿自旋）到Pccn（低自旋）的晶体对称变化，这对应于铁原子网络的强重组。在所有四种化合物中，FeN6核心的演化与温度的函数以及分子内特征几乎相同。第一个近似是，除了P2(1)/c结构形成不对称的分子环境外，所有结构的晶体填充都是相似的。然而，对分子间相互作用的仔细检查，分类为分子内和分子间，显示出一些差异。在Fe(PM-BiA)(2)(NCS)(2)和Fe(PM-PEA)(2)(NCS)(2)中，片内和片间的相互作用比在Fe(PM-TeA)(2)(NCS)(2)中没有“第二”相邻的片内接触的情况下更强，或者在Fe(PMAzA)(2)(NCS)(2)中，片间相互作用较弱。因此，过渡的突然性归因于紧密的页内和页间接触的结合。Fe(PM-PEA)(2)(NCS)(2)中的迟滞效应与高温下碳-碳分子间接触的不规则铁原子网络可能发生的相变有关，而Fe(PM-AzA)(2)(NCS)(2)中没有发现相同的不规则铁原子网络。
We have determined the crystal structures, both in high and low spin state, of four Fe(PM-L)(2)(NCS)(2) complexes, where PM is N-2'-pyridylmethylene and the aromatic subunit L is 4-aminoterphenyl (TeA), 4-(phenylazo) aniline (AzA), 4-aminobiphenyl( BiA) or 4-(phenylethynyl) aniline (PEA). As previously reported, these compounds undergo a spin crossover at low temperature with different features of transition: very smooth and incomplete for Fe(PM-TeA)(2)(NCS)(2), smooth with almost no hysteresis for Fe(PM-AzA)(2)(NCS)(2), unusually abrupt for Fe(PMBiA)(2)(NCS)(2), and abrupt with a very large hysteresis (37 K) for Fe(PM-PEA)(2)(NCS)(2). In Fe(PM-BiA)(2)(NCS)(2), Fe(PM-TeA)(2)(NCS)(2) and Fe(PM-AzA)(2)(NCS)(2) the spin conversion is not associated with a large structural phase transition and the space group is the same above and below the temperature of transition: orthorhombic Peen for the two first and monoclinic P2(1)/c for the third. On the other hand, Fe(PM-PEA)(2)(NCS)(2) undergoes a change in the crystal symmetry from P2(1)/c thigh spin) to Pccn (low spin) which corresponds to a strong re-organisation of the iron atom network. The evolution as a function of temperature of the FeN6 core as well as of the intramolecular characteristics are almost identical in all four compounds. To a first approximation, the crystal packing is similar in all of the structures except that the P2(1)/c structures develop an asymmetrical molecular environment. Nevertheless, a close examination of the intermolecular interactions, classified as intra- and inter-sheet, show some differences. The intrasheet and the intersheet interactions are stronger in Fe(PM-BiA)(2)(NCS)(2) and Fe(PM-PEA)(2)(NCS)(2) than either in Fe(PM-TeA)(2)(NCS)(2) where no 'second' neighbour intrasheet contacts are created, or in Fe(PMAzA)(2)(NCS)(2) where the intersheet interactions are weak. Thus, the abruptness of the transition is attributed to the combination of close intrasheet and intersheet contacts. The hysteresis effect in Fe(PM-PEA)(2)(NCS)(2) is connected to the phase transition which could occur due to an irregular iron atom network associated with very short carbon-carbon intermolecular contacts at high temperature, not found in Fe(PM-AzA)(2)(NCS)(2) which shows the same irregular iron atom network.