The origin of the two-electron/four-centers C[BOND]C bond in π-TCNE22 dimers: Electrostatic or dispersion?

Authors

  • Iñigo García-Yoldi,

    1. Departament de Qúmica F´sica, Facultat de Qúmica, and CERQT, Parc Cient´fic, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona, Spain
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  • Fernando Mota,

    1. Departament de Qúmica F´sica, Facultat de Qúmica, and CERQT, Parc Cient´fic, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona, Spain
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  • Juan J. Novoa

    Corresponding author
    1. Departament de Qúmica F´sica, Facultat de Qúmica, and CERQT, Parc Cient´fic, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona, Spain
    • Departament de Qúmica F´sica, Facultat de Qúmica, and CERQT, Parc Cient´fic, Universitat de Barcelona, Av. Diagonal 647, 08028-Barcelona, Spain

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Abstract

The structure and stability of the π-TCNE22 dimers in K2TCNE2 aggregates is revisited trying to find if the origin of their two-electron/four-centers C[BOND]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-TCNE22 structure has the two K+ atoms placed in equatorial positions in between the two TCNE planes. When the K+ atoms are placed along the D2h 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

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