Das Arijit, Arunan Elangannan
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India.
Phys Chem Chem Phys. 2023 Aug 30;25(34):22583-22594. doi: 10.1039/d3cp00370a.
Using correlation plots of binding energy and electron density at the bond critical point, we investigated the nature of intermolecular non-covalent bonds (D-X⋯A, where D = O/S/F/Cl/Br/H, mostly, X = main group elements (except noble gases), A = HO, NH, HS, PH, HCHO, CH, HCN, CO, CHOH, and CHOCH). The binding energies were calculated at the MP2 level of theory, followed by Atoms in Molecules (AIM) analysis of the wave functions to obtain the electron density at the bond critical point (BCP). For each non-covalent bond, the slopes of the binding energy electron density plot have been determined. Based on their slopes, non-covalent bonds are classified as non-covalent bond closed-shell (NCB-C) or non-covalent bond shared-shell (NCB-S). Intriguingly, extrapolating the slopes of the NCB-C and NCB-S cases leads to intramolecular "ionic" and "covalent" bonding regimes, establishing a link between such intermolecular non-covalent and intramolecular chemical bonds. With this new classification, hydrogen bonds and other non-covalent bonds formed by a main-group atom in a covalent molecule are classified as NCB-S. Atoms found in ionic molecules generally form NCB-C type bonds, with the exception of carbon which also forms NCB-C type bonds. Molecules with a tetravalent carbon do behave like ions in ionic molecules such as NaCl and interact with other molecules through NCB-C type bonds. As with the chemical bonds, there are some non-covalent bonds that are intermediate cases.
通过结合能与键临界点处电子密度的相关图，我们研究了分子间非共价键（D-X⋯A，其中D主要为O/S/F/Cl/Br/H，X为主族元素（稀有气体除外），A为HO、NH、HS、PH、HCHO、CH、HCN、CO、CHOH和CHOCH）的性质。结合能在MP2理论水平下计算，随后对波函数进行分子中的原子（AIM）分析，以获得键临界点（BCP）处的电子密度。对于每个非共价键，已确定结合能-电子密度图的斜率。基于这些斜率，非共价键被分类为非共价键闭壳层（NCB-C）或非共价键共享壳层（NCB-S）。有趣的是，外推NCB-C和NCB-S情况的斜率会导致分子内的“离子”和“共价”键合机制，从而在这种分子间非共价键和分子内化学键之间建立联系。通过这种新的分类，共价分子中由主族原子形成的氢键和其他非共价键被分类为NCB-S。离子分子中的原子通常形成NCB-C型键，但碳除外，碳也形成NCB-C型键。具有四价碳的分子在离子分子（如NaCl）中的行为类似于离子，并通过NCB-C型键与其他分子相互作用。与化学键一样，也有一些非共价键属于中间情况。
