Journal of Molecular Modeling

, Volume 19, Issue 6, pp 2549–2557 | Cite as

Natural bond orbital, nuclear magnetic resonance analysis and hybrid-density functional theory study of σ-aromaticity in Al2F6, Al2Cl6, Al2Br6 and Al2I6

  • Davood Nori-Shargh
  • Hooriye Yahyaei
  • Seiedeh Negar Mousavi
  • Akram Maasoomi
  • Hakan Kayi
Original Paper


Natural bond orbital (NBO), nuclear magnetic resonance (NMR) analysis and hybrid-density functional theory based method (B3LYP/Def2-TZVPP) were used to investigate the correlation between the nucleus-independent chemical shifts [NICS, as an aromaticity criterion], σ Al(1)-X2(b)σ*Al(3)-X4(b) electron delocalizations and the dissociation energies of Al2F6, Al2Cl6, Al2Br6 and Al2I6 to 2AlX3 (X = F, Cl, Br, I). The results obtained showed that the dissociation energies of Al2F6, Al2Cl6, Al2Br6 and Al2I6 decrease from Al2F6 to Al2I6. Like aromatic molecules, these compounds have relatively significant negative NICSiso(0) values. Clearly, based on magnetic criteria, they exhibit aromatic character and make it possible to consider them as σ-delocalized aromatic species, such as Möbius σ-aromatic species. The σ-aromatic character which is demonstrated by their NICSiso(0) values decreases from Al2F6 to Al2I6. The NICSiso values are dominated by the in-plane σ22 (i.e., σyy, the plane containing halogen atoms bridged) chemical shift components. The increase of the NICSiso values explains significantly the decrease of the corresponding dissociation energies of Al2F6, Al2Cl6, Al2Br6 and Al2I6. Importantly, the NBO results suggest that in these compounds the dissociation energies are controlled by the stabilization energies associated with σ Al(1)-X2(b)σ*Al(3)-X4(b) electron delocalizations. The decrease of the stabilization energies associated with σ Al(1)-X2(b)σ*Al(3)-X4(b) electron delocalizations is in accordance with the variation of the calculated NICSiso values. The correlations between the dissociation energies of Al2F6, Al2Cl6, Al2Br6 and Al2I6, σ Al(1)-X2(b)σ*Al(3)-X4(b) electron delocalizations, natural atomic orbitals (NAOs) and NICSiso values have been investigated.


Hybrid-DFT calculations Al2F6 Al2Cl6 Al2Br6 Al2I6 AM1* NBO NICS 



This research has been supported by Islamic Azad University, Arak Branch. Some parts of this work have been supported by Welch Foundation at the University of Texas at Austin, Grant No. F-100.


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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Davood Nori-Shargh
    • 1
  • Hooriye Yahyaei
    • 2
  • Seiedeh Negar Mousavi
    • 1
  • Akram Maasoomi
    • 1
  • Hakan Kayi
    • 3
    • 4
  1. 1.Department of Chemistry, Arak BranchIslamic Azad UniversityArakIran
  2. 2.Department of Chemistry, Zanjan BranchIslamic Azad UniversityZanjanIran
  3. 3.Institute for Theoretical Chemistry, Department of Chemistry and BiochemistryThe University of TexasAustinUSA
  4. 4.Department of Chemical Engineering and Applied ChemistryAtilim UniversityAnkaraTurkey

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