A Reliable Quantum-Chemical Protocol for the Characterization of Organic Mixed-Valence Compounds
A Reliable Quantum-Chemical Protocol for the Characterization of Organic Mixed-Valence Compounds
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DOI：
10.1021/ja9070859
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发表时间：
2009-11-11
影响因子：
15
通讯作者：
Kaupp, Martin
中科院分区：
文献类型：
--
作者：
Renz, Manuel;Theilacker, Kolja;Kaupp, Martin
采用混合密度泛函方法，结合连续溶剂模型和可变精确交换混合物，系统地研究了一系列混合价双三芳胺自由基阳离子的结构、偶极矩、电子转移势垒和自旋密度分布.所选择的系统不同，在他们的桥接单位，都是相对接近的，从两侧，罗宾-戴分类的混合价系统的II/III类边界。溶剂效应被发现有显着的影响，这些阳离子的本地化与离域字符。虽然气相计算或计算在非极性溶剂中的所有系统的离域III类侧，一个更极性的溶剂，如乙腈，使观察对称性破缺和电荷本地化与适度的精确交换混合物在混合功能的系统上的II类侧（与二苯基丁二炔和二苯基乙炔桥）。相反，具有最短桥的阳离子（亚苯基、亚联苯基）被表征为III类。计算的价间电荷转移激发频率与实验的比较证实了系统与二苯基丁二炔桥，并可能与二苯基乙炔桥的系统，是II类，而在二氯甲烷溶剂用于光谱测量，其他两个系统是在III类侧。非标准混合密度泛函计算与35%的Hartree-Fock交换结合连续溶剂模型建议作为一个实用的协议的量子化学表征的有机混合价体系。这种方法应该允许更仔细的检查，并提供了一个基础，其他计算方法的评价。
Structures, dipole moments, electron-transfer barriers, and spin density distributions of a series of mixed-valent bistriarylamin radical cations have been studied systematically by hybrid density functional methods with variable exact-exchange admixture combined with a continuum solvent model. The chosen systems differ in their bridging units and are all relatively close, from both sides, to the class II/III borderline of the Robin-Day classification of mixed-valence systems. Solvent effects are found to have a dramatic influence on the localized vs delocalized character of these cations. While gas-phase calculations or computations in a nonpolar solvent place all systems on the delocalized class III side, a more polar solvent like acetonitrile enables observation of symmetry breaking and charge localization with moderate exact-exchange admixtures in a hybrid functional for the systems on the class II side (with diphenylbutadiyne and diphenylethyne bridges). In contrast, the cations with the shortest bridges (phenylene, biphenylene) are characterized as class III. The comparison of computed intervalence charge-transfer excitation frequencies with experiment confirms the system with the diphenylbutadiyne bridge, and probably the system with the diphenylethyne bridge, to be class II, whereas in the dichloromethane solvent employed for spectroscopic measurements, the two other systems are on the class III side. Nonstandard hybrid density functional calculations with 35% Hartree-Fock-like exchange combined with continuum solvent models are suggested as a practical protocol for the quantum-chemical characterization of organic mixed-valence systems. This approach should allow closer examinations and provides a basis for the evaluation of other computational methods.