Tuning of chalcogen bonds by cation-π interactions: cooperative and diminutive effects.

The tunability of Y···N chalcogen bond via formation of a cation-π interaction in ternary complexes M(+)-PhYH-NH3, M(+)-PhYH-NCH, and M(+)-PhCCCN-YHF (M = Li, Na; Y = Se, Te) is investigated at MP2/aug-cc-pVDZ computational level. Our results indicate that the strength of Y···N and cation-π interactions in the ternary complexes depends on the role of the aromatic molecule. That is, a cooperative effect is evident if aromatic molecule acts as the Lewis acid and Lewis base, simultaneously, while a diminutive effect is observed when the aromatic molecule acts only as the Lewis base in both Y···N and cation-π interactions. For a given aromatic system, the shortening or lengthening of Y···N distances is more important for Li(+) complexes than Na(+) counterparts. The mechanism of cooperative/diminutive effects in the ternary complexes is studied by molecular electrostatic potential (MEP) and topological analysis of the electron density.