D(3h) [A-CE3-A]⁻ (E = Al and Ga, A = Si, Ge, Sn, and Pb): a new class of hexatomic mono-anionic species with trigonal bipyramidal carbon.
D(3h) [A-CE3-A]⁻ (E = Al and Ga, A = Si, Ge, Sn, and Pb): a new class of hexatomic mono-anionic species with trigonal bipyramidal carbon.
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DOI：
10.1063/1.4867364
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发表时间：
2014-03
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通讯作者：
Yan-Bo Wu;Yan-Qin Li;Hui Bai;Haigang Lu;Si‐Dian Li;Hua‐Jin Zhai;Zhi‐Xiang Wang
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作者：
Yan-Bo Wu;Yan-Qin Li;Hui Bai;Haigang Lu;Si‐Dian Li;Hua‐Jin Zhai;Zhi‐Xiang Wang
在亲核双分子取代反应（S（N）2）中，非经典的三角双锥碳（TBPC）排列通常以过渡态（TS）的形式存在。尽管如此，化学家们几十年来一直对这种碳键是否能在平衡结构中保持稳定感到好奇。由于理论和实验上TBPC排列通常被实现为阳离子物种，因此仅计算设计了一个阴离子实例（[At-C（CN）3-At]（-））。在这里，我们报告了一类新的阴离子TBPC物种的设计，通过使用类似的策略，用于稳定的非经典平面超配位碳。在B3 LYP和MP2水平上，当以缺电子的Al和Ga为赤道配体时，发现8个D（3 h）[A-CE 3-A]（-）（E = Al和Ga，A = Si，Ge，Sn和Pb）TBPC结构是能量最低点而不是TS。值得注意的是，CCSD（T）优化水平的能量结果进一步将[Ge-CAl 3-Ge]（-）和[Sn-CGa 3-Sn]（-）识别为全局最小值，并且将[Si-CAl 3-Si]（-）和[Ge-CGa 3-Ge]（-）识别为局部最小值，仅略高于其全局最小值。电子结构分析表明，大量的离子C-E键、外围的E-A共价键和轴向的多中心双电子（mc-2 e）键在稳定TBPC结构中起作用。结构的简单性和高的热力学稳定性表明，这些物种中的一些可以在气相中产生和捕获。此外，作为单阴离子物种，它们的第一垂直脱离能与它们最近的异构体的垂直脱离能是可区分的，这将有助于通过实验如负离子光电子能谱对其进行表征。
The non-classical trigonal bipyramidal carbon (TBPC) arrangement generally exists as transition states (TSs) in nucleophilic bimolecular substitution (S(N)2) reactions. Nevertheless, chemists have been curious about whether such a carbon bonding could be stable in equilibrium structures for decades. As the TBPC arrangement was normally realized as cationic species theoretically and experimentally, only one anionic example ([At-C(CN)3-At](-)) was computationally devised. Herein, we report the design of a new class of anionic TBPC species by using the strategy similar to that for stabilizing the non-classical planar hypercoordinate carbon. When electron deficient Al and Ga were used as the equatorial ligands, eight D(3h) [A-CE3-A](-) (E = Al and Ga, A = Si, Ge, Sn, and Pb) TBPC structures were found to be the energy minima rather than TSs at both the B3LYP and MP2 levels. Remarkably, the energetic results at the CCSD(T) optimization level further identify [Ge-CAl3-Ge](-) and [Sn-CGa3-Sn](-) even to be the global minima and [Si-CAl3-Si](-) and [Ge-CGa3-Ge](-) to be the local minima, only slightly higher than their global minima. The electronic structure analyses reveal that the substantial ionic C-E bonding, the peripheral E-A covalent bonding, and the axial mc-2e (multi center-two electrons) bonding play roles in stabilizing these TBPC structures. The structural simplicity and the high thermodynamic stability suggest that some of these species may be generated and captured in the gas phase. Furthermore, as mono-anionic species, their first vertical detachment energies are differentiable from those of their nearest isomers, which would facilitate their characterization via experiments such as the negative ion photoelectron spectroscopy.