The origin of the two-electron/four-centers CC bond in π-TCNE22− dimers: Electrostatic or dispersion?

✍ Scribed by Iñigo García-Yoldi; Fernando Mota; Juan J. Novoa

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 397 KB
• Volume: 28
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.20525

✦ Synopsis

Abstract

The structure and stability of the π‐TCNE~2~^2^^−^ dimers in K~2~TCNE~2~ aggregates is revisited trying to find if the origin of their two‐electron/four‐centers CC bond are the electrostatic K^+^‐TCNE^−^ interactions or the dispersion interactions between the anions. The study is done at the HF, B3LYP, CASSCF (2,2), and MCQDPT/CASSCF (2,2) levels using the 6‐31+G(d) basis set. Our results show that the only minima of this aggregate that preserves the π‐TCNE~2~^2^^−^ structure has the two K^+^ atoms placed in equatorial positions in between the two TCNE^−^ planes. When the K^+^ atoms are placed along the D~2__h__~ axis of the anions the structure is not a minimum. The main energetic component responsible for the stability of these aggregates comes from the cation–anion interactions. However, a proper accounting of the dispersion component (as done in the MCQDPT/CASSCF (2,2) calculations) is needed to make the closed‐shell singlet more stable than the open‐shell singlet. Thus, the bond results from the combination of the electrostatic and dispersion components, being the first the dominant one. The optimum geometry of the closed‐shell singlet is very similar to the experimental one found in crystals. © 2006 Wiley Periodicals, Inc. J Comput Chem 2007