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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electron Localization in Solid Acetonitrile
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Electron Localization in Solid Acetonitrile

机译：固体乙腈中的电子定位

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Electron localization in the bulk condensed phases of acetonitrile differs drastically from the corresponding processes that take place in water and aliphatic alcohols. In particular, electron capture following the ionization of liquid and solid acetonitrile yields well-defined radical anions in place of the largely structureless solvated and trapped electrons characteristic of irradiated solutions and rigid glasses. This is remarkable given the many similarities that exist not only between the intrinsic properties of these individual solvent molecules, such as polarity, but also in their cooperative capacity to function as solvents. Here, with the aid of detailed experimental and computational studies, we examine on a fundamental level what gives rise to such a sharp contrast in the behavior of these alkyl cyanides as compared to water and alcohols. EPR and optical spectra, and ab initio calculations on the radical anions are used together with diffraction data for the crystal structures to demonstrate that electron attachment to nitrile molecules in the crystalline state results in a significant bending of the linear CCN moiety. Moreover, in the formation of the dimer anions, which only takes place in certain crystalline phases, it is determined that the intermolecular bonding occurs between the cyanide carbons in an antiparallel arrangement. A staggered structure for the dimer anion in α-acetonitrile is then suggested, in which there is a nearly coplanar arrangement with the two bent CCN fragments. The resulting structure accounts for the observed EPR parameters, the position of the UV-vis absorption band, and the trends observed in the vibronic progressions for the four H/D isotopomers. The dimer radical anion in α-acetonitrile retains the same orientation and symmetry as that of the preexisting neutral {CH_3CN}_2 pairs in this crystal despite the resulting changes in molecular geometry and in the translational coordinates for the cyanide carbons as the two acetonitrile molecules come together. We suggest that dimer anions of nitriles can form only in the phases where such "antiparallel" pairs occur, including liquid systems; otherwise, the electron remains attached to a single molecule, as in β-acetonitrile. Because electron capture by water or alcohol molecules in the condensed phase appears to require larger molecular clusters, the contrast between the behavior of these solvents and acetonitrile is attributable to the relative ease with which acetonitrile molecules in the crystal or solvent can undergo valence-electron attachment via their accessible low-lying π~* orbitals.
机译：乙腈本体冷凝相中的电子定位与在水和脂族醇中发生的相应过程有很大不同。尤其是，液体和固体乙腈电离后的电子俘获可产生定义明确的自由基阴离子，从而取代了辐射溶液和刚性玻璃所特有的无结构溶剂化和俘获电子。鉴于不仅在这些单个溶剂分子的内在特性（例如极性）之间存在许多相似性，而且在它们作为溶剂起作用的协同能力方面还存在许多相似性，这一点非常明显。在这里，借助于详细的实验和计算研究，我们从根本上考察了与水和醇相比，这些烷基氰化物的行为形成了如此鲜明的对比。 EPR和光谱，以及自由基阴离子的从头算与晶体结构的衍射数据一起使用，以证明在结晶状态下电子与腈分子的连接导致线性CCN部分的显着弯曲。此外，在仅在某些结晶相中发生的二聚体阴离子的形成中，确定在氰化物碳之间以反平行排列发生了分子间键合。然后提出了α-乙腈中二聚体阴离子的交错结构，其中两个弯曲的CCN片段几乎处于共面排列。所得结构说明了所观察到的EPR参数，UV-vis吸收带的位置，以及四种H / D异位异构体在电子振动过程中观察到的趋势。尽管随着两个乙腈分子的到来，氰化物碳的分子几何结构和平移坐标发生了变化，但α-乙腈中的二聚自由基阴离子仍与该晶体中先前存在的中性{CH_3CN} _2对相同。一起。我们建议腈的二聚体阴离子只能在发生这种“反平行”对的相中形成，包括液相。否则，电子将保持附着在单个分子上，例如在乙乙腈中。由于冷凝相中水或醇分子的电子俘获似乎需要更大的分子簇，因此这些溶剂与乙腈的行为之间的对比可归因于晶体或溶剂中的乙腈分子可以相对容易地进行价电子附着通过它们可访问的低地π〜*轨道。

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