氨化电子作为溶剂稳定的多聚体自由基阴离子
Ammoniated electron as a solvent stabilized multimer radical anion
摘要：
液氨中的过量电子（“氨化电子”）通常被视为空穴电子，其中s型波函数填充6-9个氨分子之间的间隙空隙。在这里，我们研究了另一种模型，其中氨化电子被认为是一种溶剂稳定的多聚体自由基阴离子，如最初提出的西蒙斯[化学会评论1976年，5，337]。在这个模型中，大部分多余的电子密度驻留在形成溶剂化腔的氨分子中N原子的前线轨道中;该自旋密度的一部分被转移到第二溶剂化壳层中的分子。由于带负电荷的溶剂分子之间的排斥而形成空腔。用密度泛函理论计算气相中的小氨簇阴离子，结果表明，这些核阴离子可以半定量地解释NMR谱观察到的1-H和14-N原子核的Knight位移和红外光谱观察到的向下位移的伸缩和弯曲模式.据推测，在其他非质子溶剂（但不是在水和醇）中的过量电子可能是，在这方面，类似于氨化电子，大量转移的自旋密度到前线N和C轨道的甲基，氨基，和酰胺基团形成的溶剂化腔。
英文摘要：
The excess electron in liquid ammonia ("ammoniated electron") is commonly viewed as a cavity electron in which the s-type wave function fills the interstitial void between 6-9 ammonia molecules. Here we examine an alternative model in which the ammoniated electron is regarded as a solvent stabilized multimer radical anion, as was originally suggested by Symons [Chem. Soc. Rev. 1976, 5, 337]. In this model, most of the excess electron density resides in the frontier orbitals of N atoms in the ammonia molecules forming the solvation cavity; a fraction of this spin density is transferred to the molecules in the second solvation shell. The cavity is formed due to the repulsion between negatively charged solvent molecules. Using density functional theory calculations for small ammonia cluster anions in the gas phase, it is demonstrated that such core anions would semi-quantitatively account for the observed pattern of Knight shifts for 1-H and 14-N nuclei observed by NMR spectroscopy and the downshifted stretching and bending modes observed by infrared spectroscopy. It is speculated that the excess electrons in other aprotic solvents (but not in water and alcohols) might be, in this respect, analogous to the ammoniated electron, with substantial transfer of the spin density into the frontier N and C orbitals of methyl, amino, and amide groups forming the solvation cavity.
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