Guo Jin-Chang, Tian Wen-Juan, Wang Ying-Jin, Zhao Xue-Feng, Wu Yan-Bo, Zhai Hua-Jin, Li Si-Dian
Institute of Materials Science and Department of Chemistry, Xinzhou Teachers' University, Xinzhou, Shanxi 034000, China.
Nanocluster Laboratory, Institute of Molecular Science, Shanxi University, Taiyuan, Shanxi 030006, China.
J Chem Phys. 2016 Jun 28;144(24):244303. doi: 10.1063/1.4954658.
Superalkali cations, known to possess low vertical electron affinities (VEAs), high vertical detachment energies, and large highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gaps, are intriguing chemical species. Thermodynamically, such species need to be the global minima in order to serve as the promising targets for experimental realization. In this work, we propose the strategies of polyhalogenation and polyalkalination for designing the superalkali cations. By applying these strategies, the local-minimum planar pentacoordinate carbon (ppC) cluster CBe5 can be modified to form a series of star-like superalkali ppC or quasi-ppC CBe5X5 (+) (X = F, Cl, Br, Li, Na, K) cations containing a CBe5 moiety. Polyhalogenation and polyalkalination on the CBe5 unit may help eliminate the high reactivity of bare CBe5 molecule by covering the reactive Be atoms with noble halogen anions and alkali cations. Computational exploration of the potential energy surfaces reveals that the star-like ppC or quasi-ppC CBe5X5 (+) (X = F, Cl, Br, Li, Na, K) clusters are the true global minima of the systems. The predicted VEAs for CBe5X5 (+) range from 3.01 to 3.71 eV for X = F, Cl, Br and 2.12-2.51 eV for X = Li, Na, K, being below the lower bound of the atomic ionization potential of 3.89 eV in the periodic table. Large HOMO-LUMO energy gaps are also revealed for the species: 10.76-11.07 eV for X = F, Cl, Br and 4.99-6.91 eV for X = Li, Na, K. These designer clusters represent the first series of superalkali cations with a ppC center. Bonding analyses show five Be-X-Be three-center two-electron (3c-2e) σ bonds for the peripheral bonding, whereas the central C atom is associated with one 6c-2e π bond and three 6c-2e σ bonds, rendering (π and σ) double aromaticity. Born-Oppenheimer molecular dynamics simulations indicate that the CBe5 motif is robust in the clusters. As planar hypercoordination carbon species are often thermodynamically unstable and highly reactive, the superalkali cation characters of these ppC species should be highlighted, which may be suitable for experimental realization.
超碱阳离子因其具有低垂直电子亲和能（VEA）、高垂直脱附能以及大的最高占据分子轨道（HOMO）-最低未占据分子轨道（LUMO）能隙而成为引人关注的化学物种。从热力学角度来看，此类物种需要是全局最小值，才能成为实验实现的有前景的目标。在这项工作中，我们提出了多卤化和多碱化策略来设计超碱阳离子。通过应用这些策略，可以对局部最小平面五配位碳（ppC）簇CBe5进行修饰，以形成一系列包含CBe5部分的星状超碱ppC或准ppC CBe5X5（+）（X = F、Cl、Br、Li、Na、K）阳离子。在CBe5单元上进行多卤化和多碱化可能有助于通过用惰性卤素阴离子和碱金属阳离子覆盖活性Be原子来消除裸CBe5分子的高反应性。势能面的计算探索表明，星状ppC或准ppC CBe5X5（+）（X = F、Cl、Br、Li、Na、K）簇是系统的真正全局最小值。对于X = F、Cl、Br，CBe5X5（+）的预测VEA范围为3.01至3.71 eV，对于X = Li、Na、K，范围为2.12 - 2.51 eV，低于元素周期表中3.89 eV的原子电离势下限。这些物种还显示出大的HOMO - LUMO能隙：对于X = F、Cl、Br为10.76 - 11.07 eV，对于X = Li、Na、K为4.99 - 6.91 eV。这些设计的簇代表了第一系列以ppC为中心的超碱阳离子。键合分析表明，外围键合有五个Be - X - Be三中心两电子（3c - 2e）σ键，而中心C原子与一个6c - 2e π键和三个6c - 2e σ键相关联，呈现（π和σ）双重芳香性。玻恩 - 奥本海默分子动力学模拟表明，CBe5 motif在簇中是稳定的。由于平面超配位碳物种通常在热力学上不稳定且反应性高，这些ppC物种的超碱阳离子特性应予以突出，这可能适合实验实现。
