Department of Chemistry and Chemical Biology, Cornell University, Baker Laboratory, Ithaca, NY 14853, USA.
Angew Chem Int Ed Engl. 2009;48(44):8198-232. doi: 10.1002/anie.200900373.
A detailed molecular orbital (MO) analysis of the structure and electronic properties of the great variety of species in lithium-ammonia solutions is provided. In the odd-electron, doublet states we have considered: e-@(NH3)n (the solvated electron, likely to be a dynamic ensemble of molecules), the Li(NH3)4 monomer, and the [Li(NH3)4+.e-@(NH3)n] ion-pairs, the Li 2s electron enters a diffuse orbital built up largely from the lowest unoccupied MOs of the ammonia molecules. The singly occupied MOs are bonding between the hydrogen atoms; we call this stabilizing interaction H-->H bonding. In e-@(NH3)n the odd electron is not located in the center of the cavities formed by the ammonia molecules. Possible species with two or more weakly interacting electrons also exhibit H-->H bonding. For these, we find that the singlet (S=0) states are slightly lower in energy than those with unpaired (S=1, 2...) spins. TD-DFT calculations on various ion-pairs show that the three most intense electronic excitations arise from the transition between the SOMO (of s pseudosymmetry) into the lowest lying p-like levels. The optical absorption spectra are relatively metal-independent, and account for the absorption tail which extends into the visible. This is the source of Sir Humphry Davy's "fine blue colour" first observed just over 200 years ago.
提供了对锂氨溶液中各种物种的结构和电子性质的详细分子轨道（MO）分析。在奇数电子、双重态中，我们考虑了：e-@(NH3)n（溶剂化电子，可能是分子的动态集合）、Li(NH3)4 单体和[Li(NH3)4+.e-@(NH3)n]离子对，Li 2s 电子进入由氨分子的最低未占据 MO 组成的弥散轨道。单占据 MO 之间的成键发生在氢原子之间；我们将这种稳定相互作用称为 H->H 键合。在 e-@(NH3)n 中，奇数电子不位于氨分子形成的腔中心。可能存在两个或更多弱相互作用电子的物种也表现出 H->H 键合。对于这些，我们发现单重态（S=0）的能量略低于具有未配对（S=1、2...）自旋的状态。对各种离子对的 TD-DFT 计算表明，三个最强烈的电子激发来自于从 SOMO（s 伪对称性）到最低的 p 类似能级的跃迁。光学吸收光谱相对独立于金属，解释了延伸到可见光的吸收尾部。这就是 Sir Humphry Davy 首先观察到的 200 多年前的“细蓝颜色”的来源。
