Bickelhaupt F Matthias, Solà Miquel, Fonseca Guerra Célia
Theoretische Chemie, Scheikundig Laboratorium der Vrije Universiteit, De Boelelaan 1083, 1081HV, Amsterdam, The Netherlands.
J Mol Model. 2006 Jul;12(5):563-8. doi: 10.1007/s00894-005-0056-0. Epub 2006 Jan 13.
We have carried out a theoretical investigation of the methyl alkali metals CH3 M with M=Li, Na, K and Rb using density functional theory (DFT) at the BP86/TZ2P level. Our purpose is to determine how the structure and thermochemistry (e.g., C-M bond lengths and strengths) of these organoalkali metal compounds depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The C-M bond becomes longer and weaker if one goes from Li to the more electropositive Rb. Also, the polarity of the C-M bond increases along this series but it preserves a strong intrinsic preference to homolytic over ionic dissociation in the gas phase. We show that a description of the bonding mechanism in terms of a polar C-M electron-pair bond between the methyl radical and alkali metal atom is just as natural as an ionic description (i.e., in terms of CH3-+M+) and that it provides a straightforward way of understanding all observed trends.
我们使用密度泛函理论（DFT）在BP86/TZ2P水平上对甲基碱金属CH3M（M = Li、Na、K和Rb）进行了理论研究。我们的目的是确定这些有机碱金属化合物的结构和热化学性质（例如，C-M键长和强度）如何依赖于金属原子，并根据定量的Kohn-Sham分子轨道（KS-MO）理论理解出现的趋势。如果从Li到电正性更强的Rb，C-M键会变长且变弱。此外，C-M键的极性沿此系列增加，但在气相中它仍强烈倾向于均裂而非离子解离。我们表明，用甲基自由基与碱金属原子之间的极性C-M电子对键来描述键合机制与离子描述（即根据CH3- + M+）一样自然，并且它提供了一种理解所有观察到的趋势的直接方法。
