Department of Chemistry, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA.
Noyes Laboratory of Chemical Physics and the Beckman Institute, California Institute of Technology, Pasadena, CA, 91125, USA.
Angew Chem Int Ed Engl. 2017 Aug 7;56(33):9897-9900. doi: 10.1002/anie.201705738. Epub 2017 Jul 18.
Both hydrogen bonding (HB) and halogen bonding (XB) are essentially electrostatic interactions, but whereas hydrogen bonding has a well-documented record of stabilizing unstable anions, little is known about halogen bonding's ability to do so. Herein, we present a combined anion photoelectron spectroscopic and density functional theory study of the halogen bond-stabilization of the pyrazine (Pz) anion, an unstable anion in isolation due to its neutral counterpart having a negative electron affinity (EA). The halogen bond formed between the σ-hole on bromobenzene (BrPh) and the lone pair(s) of Pz significantly lowers the energies of the Pz(BrPh) and Pz(BrPh) anions relative to the neutral molecule, resulting in the emergence of a positive EA for the neutral complexes. As seen through its charge distribution and electrostatic potential analyses, the negative charge on Pz is diluted due to the XB. Thermodynamics reveals that the low temperature of the supersonic expansion plays a key role in forming these complexes.
氢键（HB）和卤键（XB）本质上都是静电相互作用，但氢键在稳定不稳定阴离子方面有很好的记录，而卤键在这方面的能力则知之甚少。在此，我们结合阴离子光电子能谱和密度泛函理论研究了吡嗪（Pz）阴离子的卤键稳定作用，由于其中性对应物具有负电子亲合能（EA），因此 Pz 阴离子在孤立状态下是不稳定的阴离子。溴苯（BrPh）上的 σ 空穴和 Pz 的孤对之间形成的卤键显著降低了 Pz（BrPh）和 Pz（BrPh）阴离子的能量，相对于中性分子，导致中性配合物出现正 EA。通过其电荷分布和静电势分析可以看出，由于 XB，Pz 上的负电荷被稀释。热力学表明，超音速膨胀的低温在形成这些配合物方面起着关键作用。
