MOLECULAR DESIGN AND MODEL EXPERIMENTS OF FERROMAGNETIC INTERMOLECULAR INTERACTION IN THE ASSEMBLY OF HIGH-SPIN ORGANIC-MOLECULES - GENERATION AND CHARACTERIZATION OF THE SPIN STATES OF ISOMERIC BIS(PHENYLMETHYLENYL)[2.2]PARACYCLOPHANES
MOLECULAR DESIGN AND MODEL EXPERIMENTS OF FERROMAGNETIC INTERMOLECULAR INTERACTION IN THE ASSEMBLY OF HIGH-SPIN ORGANIC-MOLECULES - GENERATION AND CHARACTERIZATION OF THE SPIN STATES OF ISOMERIC BIS(PHENYLMETHYLENYL)[2.2]PARACYCLOPHANES
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DOI：
10.1021/ja00243a014
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发表时间：
1987-04-29
影响因子：
15
通讯作者：
IWAMURA, H
中科院分区：
文献类型：
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作者：
IZUOKA, A;MURATA, S;IWAMURA, H
本文用ESR谱研究了[2.2]对环蕃骨架中两个三重态二苯基卡宾单元之间的电子自旋-自旋相互作用。制备了假邻位、假间位和假对位二重氮[2.2]对环芳（4a-c），并在2-甲基四氢呋喃玻璃中低温下用Pyrex过滤的紫外光光解，得到相应的二卡宾（5a-c）。强烈的五重奏信号，|- -|= 0.0624，|£| = 0.0190 cm™ 1。在11-50 K温度范围内，它们的强度服从居里定律，表明五重态5a是基态。在高于20 K的温度下，还检测到由于热填充三重态而产生的104.0 mT的信号。从其强度的温度依赖性的分析，三重态位于能级0.18千卡/摩尔以上的五重态。Pseudometa bis（phenylmethylenyl）[2.2] paracyclophane（5 b）在11 K时没有ESR信号。在黑暗中，当温度升高到25 K以上时，出现了一组三重态信号，|D| = 0.1840，|£| = 0.0023 cm™ 1出现。因此，发现5 b处于单重基态，并且其热填充三重态在基态以上0.28 kcal/mol。高强度的五重信号（|Z）|= 0.1215 cm-1，|ε = 0.0085 cm™ 1），但它在化学上太不稳定，无法研究居里曲线。偶极相互作用张量已计算所得的五重态的二卡宾5a和5c和三重态的二卡宾5 b。计算的零场分裂参数与实验产生的建议的二卡宾的构象的最佳拟合。McConnell关于两个有机自由基之间的分子间磁相互作用的理论得到了证明，并发现了一种增加高自旋芳香分子维数的新策略，有机铁磁体的分子设计和构筑是现代理论化学和有机化学的重要研究课题。1作为实现这一具有挑战性目标的一种方法，我们通过在低温下光解相应的重氮化合物，产生了一系列高自旋聚卡宾。2磁化率的测量表明，四卡宾PhC（m-C_6 H_4C）_3 Ph具有很大的顺磁性，接近超顺磁性。[3]这一发现的逻辑延伸是，将有可能构建“有机分子磁体”。居里曲线的顺磁磁化率的样品在2-甲基四氢呋喃（2 MTHF）的玻璃或在纯晶体显示，然而，在偶然形成的聚集体的分子间相互作用是反铁磁性的。因此，必须在整个分子组装中建立宏观尺度的自旋排列，设计一个分子间相互作用可以是铁磁性的系统。实现这一目标的一个合理的方法是在晶体和其他有组织的分子系统中设计含自旋芳环的分子堆叠;这将在本文中讨论。让我们来讨论两个三重态分子之间的弱分子间相互作用，产生单重态、三重态和五重态。图14当两个变量之间的交换积分（J）
The electron spin-spin interaction between the two triplet diphenylcarbene units incorporatedin the [2.2] paracyclophane skeleton has been investigated by ESR spectroscopy. Pseudoortho, pseudometa, and pseudopara didiazo [2.2] paracyclophanes (4a-c) were prepared and photolyzed with Pyrex-filtered UV light in a 2-methyltetrahydrofuran glass atcryogenic temperatures to give the corresponding dicarbenes (5a-c). Intense quintet signals with|£>|= 0.0624 and|£|= 0.0190 cm™ 1 were obtained from 4a. Their intensity obeyed the Curie law in the temperature range 11-50 K, showing that quintet 5a was the ground state. A signal at 104.0 mT due to the thermally populated triplet was also detected at temperatures above 20 K. From the analysis of the temperature dependence of its intensity, the triplet state was located at the energy level 0.18 kcal/mol above the quintet state. Pseudometa bis (phenylmethylenyl)[2.2] paracyclophane (5b) did not show anyESR signal at 11 K. As the temperature was raised above25 K inthe dark, a set of triplet signals with| D|= 0.1840 and|£|= 0.0023 cm™ 1 appeared. Thus it was found that 5b was in the singlet ground state, and its thermally populated triplet was at 0.28 kcal/mol above the ground state. Intense quintet signals (| Z)|= 0.1215 cm'1 and|£= 0.0085 cm™ 1) were detected at 15 K for 5c, but it was too unstable chemically to study the Curie plots. Dipolar interaction tensors have been calculated for the resultant quintet states of dicarbenes 5a and 5c and the triplet state of dicarbene 5b. The best fit of the computed zero-field splitting parameters with those of the experiments produced proposed conformations of the dicarbenes. McConnell’s theory on the intermolecular magnetic interaction between two organic radicals has been demonstrated and a new strategy for increasing the dimension of the high-spin aromatic molecules was found.Molecular design and constructionof organic ferromagnets are the subject of great interest inmodern theoretical and organic chemistry. 1 As an approach to this challenging goal, we have generated a series of high-spinpolycarbenes by photolysis of the corresponding polydiazo compounds at cryogenic temperatures. 2 Magnetic susceptibility measurements have revealed that the nonent tetracarbene PhC (m-C6H4C) 3Ph, for example, has the paramagnetic property of a very large magnetic moment, ap-proaching superpara-magnetism. 3 The logical extension of this finding is that it will be possible to construct “organic molecular magnets”. Curie plots of the paramagnetic susceptibility of a sample in 2-methyltetrahydrofuran (2MTHF) glass or in neat crystal have shown, however, that the intermolecular interactions in the fortuitously formed aggregates are antiferromagnetic. Therefore, it is imperative for establishing thespin alignment in macroscopic scale throughout the molecular assembly that a system be designed in which intermolecular interactions could be ferromagnetic. One of the plausible methods for achieving this objective is a design of molecularstacking of the spin-containing aromatic rings in crystalsand other organized molecular systems; 4 this will be discussed in this paper. Let us treat the problem of weak intermolecular interaction between two triplet molecules, generating the singlet, triplet, and quintet states. 14 When the exchange integral (J) between the two