Department of Chemistry, State University of New York at Buffalo, 331 Natural Sciences Complex, Buffalo, New York 14260, United States.
J Am Chem Soc. 2011 Mar 16;133(10):3535-47. doi: 10.1021/ja109397k. Epub 2011 Feb 22.
The highly expanded metal, lithium(0)tetraamine, and its electronic structure is as full of complexity and surprises as the lithium solutions in anhydrous ammonia from which it crystallizes at 90 K. Our theoretical studies of the Phase II, Z = 8, I43d structure of this material reveal that the molecular building block is an almost ideal tetrahedron, in agreement with recent experiments. Close in enthalpy at P = 1 atm, and consistent with the low melting point, are bcc and Cs-IV configurations. Under pressure, the I43d structure emerges as more stable than its alternatives. In this phase six relatively narrow bands, four of them occupied, separate from the conduction and valence bands. We trace these bands to pockets of electron density arising between sterically encumbered ammonias, six such pockets in the Z = 8 unit cell. The observed band structure can be explained by considering a Jortner-type model, where pseudoatoms are placed in these holes. The electride Li(NH(3))(4), while not a very good metal, is a unique material, by virtue of its low melting point.
高度扩展的金属锂四胺及其电子结构充满了复杂性和惊喜，就像从无水氨中结晶出的锂溶液一样，在 90 K 下结晶。我们对这种材料的 II 相（Z=8，I43d 结构）的理论研究表明，分子构建块是一个几乎理想的四面体，与最近的实验结果一致。在 P=1 atm 下，焓值相近，且与低熔点一致的是 bcc 和 Cs-IV 构型。在压力下，I43d 结构比其替代结构更稳定。在这个相中，六个相对较窄的能带，其中四个被占据，与导带和价带分离。我们将这些能带追溯到氨之间空间位阻产生的电子密度口袋，在 Z=8 的单位晶胞中有六个这样的口袋。通过考虑 Jortner 型模型，可以解释观察到的能带结构，在该模型中，伪原子被放置在这些孔中。尽管锂氮化物 Li(NH3)4 不是一种很好的金属，但由于其低熔点，它是一种独特的材料。
