Structure and bonding of methyl alkali metal molecules.
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.
Bickelhaupt
F Matthias
FM
Theoretische Chemie, Scheikundig Laboratorium der Vrije Universiteit, De Boelelaan 1083, 1081HV, Amsterdam, The Netherlands. FM.Bickelhaupt@few.vu.nl
Solà
Miquel
M
Fonseca Guerra
Célia
C
D008672:Metals, Alkali / Q000737:chemistry*; D008745:Methylation; D008968:Molecular Conformation
D008672:Metals, Alkali