Get access

Halogen Bonding from a Hard and Soft Acids and Bases Perspective: Investigation by Using Density Functional Theory Reactivity Indices

Authors

  • Dr. Balazs Pinter,

    1. Eenheid Algemene Chemie (ALGC), Member of the QCMM VUB-UGent Alliance Research Group, Vrije Universiteit Brussel, Pleinlaan 2, Brussels (Belgium), Fax: (+32) 26293317
    Search for more papers by this author
  • Nick Nagels,

    1. Cryospectroscopy Research group Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp (Belgium), Fax: (+32) 32653320
    Search for more papers by this author
  • Prof. Wouter A. Herrebout,

    Corresponding author
    1. Cryospectroscopy Research group Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp (Belgium), Fax: (+32) 32653320
    • Cryospectroscopy Research group Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp (Belgium), Fax: (+32) 32653320
    Search for more papers by this author
  • Prof. Frank De Proft

    Corresponding author
    1. Eenheid Algemene Chemie (ALGC), Member of the QCMM VUB-UGent Alliance Research Group, Vrije Universiteit Brussel, Pleinlaan 2, Brussels (Belgium), Fax: (+32) 26293317
    • Eenheid Algemene Chemie (ALGC), Member of the QCMM VUB-UGent Alliance Research Group, Vrije Universiteit Brussel, Pleinlaan 2, Brussels (Belgium), Fax: (+32) 26293317
    Search for more papers by this author

Abstract

Halogen bonds between the trifluoromethyl halides CF3Cl, CF3Br and CF3I, and dimethyl ether, dimethyl sulfide, trimethylamine and trimethyl phosphine were investigated using Pearson’s hard and soft acids and bases (HSAB) concept with conceptual DFT reactivity indices, the Ziegler–Rauk-type energy-decomposition analysis, the natural orbital for chemical valence (NOCV) framework and the non-covalent interaction (NCI) index. It is found that the relative importance of electrostatic and orbital (charge transfer) interactions varies as a function of both the donor and acceptor molecules. Hard and soft interactions were distinguished and characterised by atomic charges, electrophilicity and local softness indices. Dual-descriptor plots indicate an orbital σ hole on the halogen similar to the electrostatic σ hole manifested in the molecular electrostatic potential. The predicted high halogen-bond-acceptor affinity of N-heterocyclic carbenes was evidenced in the highest complexation energy for the hitherto unknown CF3I⋅NHC complex. The dominant NOCV orbital represents an electron-density deformation according to a n→σ*-type interaction. The characteristic signal found in the reduced density gradient versus electron-density diagram corresponds to the non-covalent interaction between contact atoms in the NCI plots, which is the manifestation of halogen bonding within the NCI theory. The unexpected C[BOND]X bond strengthening observed in several cases was rationalised within the molecular orbital framework.

Ancillary