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Contribution of Different Crystal Packing Forces in π-Stacking: From Noncovalent to Covalent Multicentric Bonding
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2019-09-10 , DOI: 10.1021/acs.cgd.9b00540
Krešimir Molčanov 1 , Valentina Milašinović 1 , Biserka Kojić-Prodić 1
Affiliation  

The present review is aimed to compare crystal packing interactions contributing to stacking arrangements of primarily nonaromatic systems referring only briefly to classical aromatic stacking. The classical aromatic stacking is mainly based on weak dispersion interactions (E ≤ 1 kcal mol–1) whereas heteroaromatics reveal more electrostatic (or specifically dipolar) contributions (E = 5–10 kcal mol–1). Based mainly on our charge density studies and DFT calculations, the results show that (i) all planar rings stack, regardless of aromaticity (or delocalization of π electrons) and (ii) stacking interactions cover a wide continuum ranging from weak, mainly dispersion interactions (E < 5 kcal mol–1) to unlocalized two-electron multicentric (2e/mc) covalent bonds (“pancake bonds”, E > 15 kcal mol–1). Our recent studies showed that quinones form face-to-face stacks and the energies of interactions exceed 10 kcal mol–1; ours and other authors’ results indicate that interactions between planar radicals involve a significant contribution of covalent bonding. Thus, π-interactions cover a broad range of energies, ranging from ≤1 to ≥20 kcal mol–1, and the interactions span from weak dispersion to multicentric covalent bonding. Therefore, development of a universal model of stacking is needed. In this respect, stacking can be compared to hydrogen bonding, which also ranges between dispersion (weakest hydrogen bonds, such as C–H···S and C–H···Cl) and two-electron/three-centric covalent bonding (the strongest “symmetrical” hydrogen bonds).

中文翻译:

π堆积中不同晶体堆积力的贡献:从非共价键到共价多中心键

本综述旨在比较仅主要涉及经典芳族堆积的主要非芳族体系堆积安排中的晶体堆积相互作用。经典的芳香堆叠主要是基于弱色散相互作用(ë ≤1千卡摩尔-1),而杂揭示多个静电(或特异性偶极)的贡献(Ë = 5-10千卡摩尔-1)。主要基于我们的电荷密度研究和DFT计算,结果表明(i)所有平面环堆叠,无论芳香性(或π电子的离域)如何,以及(ii)堆叠相互作用涵盖了从弱的,主要是色散相互作用的广泛连续体(E <5 kcal mol –1)连接到未定位的双电子多中心(2e / mc)共价键(“薄饼键”,E > 15 kcal mol –1)。我们最近的研究表明,醌形成面对面的堆叠,相互作用的能量超过10 kcal mol –1;我们和其他作者的结果表明,平面自由基之间的相互作用涉及共价键的显着贡献。因此,π相互作用涵盖了范围广泛的能量,范围从≤1到≥20kcal mol –1,相互作用范围从弱分散到多中心共价键。因此,需要开发通用的堆叠模型。在这方面,可以将堆叠与氢键进行比较,氢键也可以在分散(最弱的氢键,例如C–H··S和C–H···Cl)和两电子/三中心共价键之间进行比较。 (最强的“对称”氢键)。
更新日期:2019-09-10
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