Theoretical study of X · 1 · YF (1 = triazine, X = Cl, Br and I, Y = H, Cl, Br, I, PH and AsH): noncovalently electron-withdrawing effects on anion-arene interactions.

The ternary complexes X · 1 · YF ( 1 = triazine, X = Cl, Br and I, Y = H, Cl, Br, I, PH and AsH) have been investigated by MP2 calculations to understand the noncovalently electron-withdrawing effects on anion-arene interactions. The results indicate that in binary complexes ( 1 · X), both weak σ-type and anion-π complexes can be formed for Cl and Br, but only anion-π complex can be formed for I. Moreover, the hydrogen-bonding complex is the global minimum for all three halides in binary complexes. However, in ternary complexes, anion-π complex become unstable and only σ complex can retain in many cases for Cl and Br. Anion-π complex keeps stable only when YF = HF. In contrast with binary complexes, σ complex become the global minimum for Cl and Br in ternary complexes. These changes in binding mode and strength are consistent with the results of covalently electron-withdrawing effects. However, in contrast with the covalently electron-withdrawing substituents, Cl and Br can attack the aromatic carbon atom to form a strong σ complex when the noncovalently electron-withdrawing effect is induced by halogen bonding. The binding behavior for I is different from that for Cl and Br in two aspects. First, the anion-π complex for I can also keep stable when the noncovalent interaction is halogen bonding. Second, the anion-π complex for I is the global minimum when it can retain as a stable structure. [ABSTRACT FROM AUTHOR]