Theoretical study of interactions between halogen-substituted s-triazine and halide anions.

The interactions between halogen-substituted s-trazine (C3H2N3X) and halide anions (Y(-)) have been investigated at the MP2/aug-cc-pVDZ (aug-cc-pVDZ-PP) level. C3H2N3X can interact with halide anions to form five types of complexes (C3H2N3X·Y(-)): a strong σ-type interaction complex, a weak σ-type interaction complex, an anion-π interaction complex, a hydrogen-bonding complex, and a halogen-bonding complex. The binding energies, structures, and bonding characteristics of these complexes have been discussed. The local details of potential energy surfaces around the binding sites for some selected complexes have been depicted. The results indicate that the binding behavior of F(-) is quite different from that of Cl(-), Br(-), and I(-). The potential energy surface is separated into two parts, the HB-σ-π region and the XB region, by a relatively high energy barrier for complexes C3H2N3Cl·Cl(-), C3H2N3Br·Cl(-), and C3H2N3I·Cl(-). The HB-σ-π region is characterized by the flat potential energy surface, indicating that the binding strength is retained when the anion is held over the HB-σ-π region. The XB region is characterized by the steeper potential energy surface, indicating that the binding strength is more sensitive to the anion position in this region. The binding strength of the HB-σ-π region is stronger than that of the XB region for C3H2N3Cl·Cl(-) and C3H2N3Br·Cl(-), whereas the binding strength of the XB region is stronger than that of the HB-σ-π region for C3H2N3I·Cl(-).