Evidence of σ- and π-Dimerization in a Series of Phenalenyls
Evidence of σ- and π-Dimerization in a Series of Phenalenyls
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DOI：
10.1021/ja509243p
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发表时间：
2014-12-31
影响因子：
15
通讯作者：
Kertesz, Miklos
中科院分区：
文献类型：
--
作者：
Mou, Zhongyu;Uchida, Kazuyuki;Kertesz, Miklos
苯酚基及其多种衍生物形成稳定的自由基，这些自由基通常以各种聚集体的形式结合，具有磁性和高导电性等有趣的特性。两种主要的聚集模式涉及p-堆积饼状多中心键形成和s-键形成。我们通过计算和实验方法探索了六种苯酚衍生物的各种 s-和 p-二聚体的能量学。现代密度泛函理论 (M05-2X) 用于测量势能表面，揭示聚集机制。为了丰富实验数据，新制备了三苯基和三甲基衍生物，并通过ESR、H-1 NMR、UVvis和单晶X射线衍射等多种分析方法研究了它们的聚集行为。计算和实验之间的一致性非常好，构成了描述本系列趋势的基础。我们发现 p-二聚体的形成可以通过单体的异步协同路径进行，也可以通过 s-二聚体的逐步过程进行。 p 堆积饼状相互作用的强度很大程度上取决于取代基，并且在结合能和接触距离方面涵盖了广泛的范围。 p 堆积二聚体中的自旋密度反映了这些趋势并显示出广泛的双自由基特征。许多 s-二聚体构型相互竞争，其中一些构型被小屏障隔开，导致 s-键合构型或 s-键合构型和 pi-键合构型之间的流动结构。
Phenalenyl and a wide variety of its derivatives form stable radicals, which often associate in various aggregates with interesting properties that include magnetism and high electrical conductivity. The two main modes of aggregation involve p-stacking pancake multicenter bond formation and s-bond formation. We explore the energetics of the various s- and p-dimers for six phenalenyl derivatives with both computational and experimental methods. A modern density functional theory (M05-2X) is used to survey the potential energy surface revealing the mechanism of the aggregation. In order to enrich experimental data, the triphenyl and trimethyl derivatives are newly prepared and their aggregation behaviors are investigated by various analytical methods including ESR, H-1 NMR, UVvis, and single-crystal X-ray diffraction. The agreement between computations and experiments are very good forming the basis of describing trends in this series. We find that p-dimer formation can proceed via an asynchronous concerted path from the monomers or in a stepwise process via s-dimers. The strength of the p-stacking pancake interaction depends strongly on substituents and covers a wide range both in terms of binding energies and contact distances. The spin densities in the p-stacking dimers reflect these trends and display a wide range of diradicaloid characters. Many s-dimer configurations compete some of which are separated by small barriers leading to fluxional structures between sigma-bonded configurations or s- and pi-bonded configurations.