Xi Jinyang, Xu Xin
Collaborative Innovation Center of Chemistry for Energy Materials, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, MOE Laboratory for Computational Physical Science, Department of Chemistry, Fudan University, Shanghai, 200433, People's Republic of China.
Phys Chem Chem Phys. 2016 Mar 7;18(9):6913-24. doi: 10.1039/c5cp08065g. Epub 2016 Feb 16.
Anion-π interaction is a new type of non-covalent interaction. It has attracted growing interest in recent years both theoretically and experimentally. However, the nature of bonding between an anion and an electron-deficient aromatic system has remained elusive. To understand the bonding nature in depth, we have carried out a systematic computational study, using model systems that involve tetraoxacalix[2]arene[2]triazine 1, an electron-deficient macrocyclic host, and four anions, X(-) (X(-) = SCN(-), NO3(-), BF4(-), and PF6(-)), of varied sizes and shapes. The geometries for the 1·X(-) complexes were optimized using the extended ONIOM (XO) method. The good agreements with the X-ray experimental results provide a validation of our theoretical schemes. The nature of the non-covalent interactions was analyzed with the help of the AIM (atoms in molecules), RDG (reduced density gradient) and LMO-EDA (local molecular orbital-energy decomposition analysis) methods. The results clearly reveal the involvement of anion-π bonding, as well as a weak, yet significant, hydrogen bonding interaction between the benzene C-H on 1 and the anion of NO3(-) or PF6(-). The bonding energies of 1·X(-) were calculated with the XYG3 functional, and the results were compared with those from MP2, M06-2X and some other functionals with non-covalent interaction corrections (e.g., B3LYP-D3, and ωB97X-D). We conclude that the binding strengths follow the order of 1·NO3(-) > 1·SCN(-) > 1·BF4(-) > 1·PF6(-), where the difference between 1·SCN(-) and 1·BF4(-) is less significant. The strongest interaction in 1·NO3(-) comes from: (1) the effective electronic interaction between NO3(-) and the triazine rings on 1; and (2) the weak hydrogen bonding interaction between the benzene C-H on 1 and nitrate, which cooperates with the anion-π interactions.
阴离子-π相互作用是一种新型的非共价相互作用。近年来，它在理论和实验方面都引起了越来越多的关注。然而，阴离子与缺电子芳香体系之间的键合本质仍然难以捉摸。为了深入理解键合本质，我们进行了一项系统的计算研究，使用了包含四氧杂杯[2]芳烃[2]三嗪1（一种缺电子大环主体）和四种不同尺寸和形状的阴离子X(-)（X(-)=SCN(-)、NO3(-)、BF4(-)和PF6(-)）的模型体系。使用扩展的ONIOM(XO)方法优化了1·X(-)配合物的几何结构。与X射线实验结果的良好吻合验证了我们的理论方案。借助AIM（分子中的原子）、RDG（约化密度梯度）和LMO-EDA（局域分子轨道-能量分解分析）方法分析了非共价相互作用的本质。结果清楚地揭示了阴离子-π键合的参与，以及1上苯环C-H与NO3(-)或PF6(-)阴离子之间微弱但显著的氢键相互作用。使用XYG3泛函计算了1·X(-)的结合能，并将结果与MP2、M06-2X以及其他一些具有非共价相互作用校正的泛函（如B3LYP-D3和ωB97X-D）的结果进行了比较。我们得出结论，结合强度遵循1·NO3(-)>1·SCN(-)>1·BF4(-)>1·PF6(-)的顺序，其中1·SCN(-)和1·BF4(-)之间的差异不太显著。1·NO3(-)中最强的相互作用来自：(1)NO3(-)与1上三嗪环之间有效的电子相互作用；(2)1上苯环C-H与硝酸根之间微弱的氢键相互作用，它与阴离子-π相互作用协同作用。
