Biferrocene-M(mnt)2 charge-transfer complexes (M = Ni, Co; mnt maleonitriledithiolate). Structure, valence states, and magnetic properties
Biferrocene-M(mnt)2 charge-transfer complexes (M = Ni, Co; mnt maleonitriledithiolate). Structure, valence states, and magnetic properties
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DOI：
10.1021/ic048285u
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发表时间：
2005-11-14
影响因子：
4.6
通讯作者：
Mori, H
中科院分区：
文献类型：
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作者：
Mochida, T;Takazawa, K;Mori, H
合成了支链烷基双二茂铁[Ni（mnt）（2）]（1a，R =异丙基; 2a，R =二新戊基）和[Co（mnt）（2）]（1b，R =异丙基; 2b，R =二新戊基）的电荷转移盐。用X射线晶体学和穆斯堡尔谱研究了它们的价态。配合物1a和1b显示出含有受体柱的偏析堆叠晶体结构，而含有大体积供体的2a和2b的结构是相当离散的。所有的配合物含有混合价的双二茂铁一价阳离子。发现配合物1a存在两步价态转变。该晶体含有两个晶体对数独立的阳离子：一个在室温以下进行价局域化，另一个在约100 ℃以下进行价局域化。十三万前一个转变是来自周围的阳离子的晶体环境的不对称性，而后者是由对称性降低加上与受体的二聚化相关的自旋Peierls转变（T-C = 133.2 K）。发现该化合物表现出基于价态互变异构的介电响应。其他配合物（1b、2a和2b）显示出价态俘获态。在所有的复合物中，发现通过供体的阳离子部分和受体的电负性部分之间的局部静电相互作用发生电荷本地化。
Charge-transfer salts of branched-alkyl biferrocenes, (1', 1"'-R-2-1,1"-biferrocene)[Ni(mnt)(2)] (1a, R = isopropyl; 2a, R = dineopentyl) and (1', 1"'-R2-1,1"-biferrocene)(2)[Co(mnt)(2)](2) (1b, R = isopropyl; 2b, R = dineopentyl), were prepared. Their valence states were investigated using X-ray crystallography and Mossbauer spectroscopy. Complexes 1a and 1b show segregated-stack crystal structures that contain columns of acceptors, whereas structures of 2a and 2b, which contain bulky donors, are rather discrete. All of the complexes contain mixed-valent biferrocenium monocations. A two-step valence transition was found in complex 1a. The crystal contains two crystal log raphically independent cations: one undergoes valence localization below room temperature; the other undergoes valence localization below ca. 130 K. The former transition is derived from asymmetry of the crystal environment around the cation, whereas the latter one is caused by symmetry lowering coupled with a spin-Peierls transition (T-C = 133.2 K) associated with the dimerization of the acceptors. This compound was found to exhibit a dielectric response based on valence tautomerization. Other complexes (1b, 2a, and 2b) show a valence-trapped state. In all complexes, charge localization was found to occur through local electrostatic interactions between the donor's cationic moiety and the acceptor's electronegative moieties.