Theoretical study of X- · 1 · YF (1 = triazine, X = Cl, Br and I, Y = H, Cl, Br, I, PH_2 and AsH_2): noncovalently electron-withdrawing effects on anion-arene interactions

摘要

The ternary complexes X- · 1 · YF (1 = triazine, X = Cl, Br and I, Y = H, Cl, Br, I, PH2 and AsH_2) 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 electronwithdrawing 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.