A B3LYP and MP2 theoretical investigation on the cooperativity effect between the XH⋯HM (X = F, Cl, Br; M = Li, Na, K) dihydrogen-bonding and HM⋯π interactions involving C6H6

The DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) calculations were carried out on the binary complex formed by HM (M = Li, Na, K) and XH (X = F, Cl, Br) or C6H6, as well as the ternary system XH⋯HM⋯C6H6. The cooperativity effect between the dihydrogen-bonding and HM⋯π interactions was investigated. The result shows that the H⋯H and HM⋯π interactions are strengthened in the ternary complex in comparison with those in the corresponding binary system. The cooperativity effect of the dihydrogen bond on the HM⋯π interaction is more pronounced than that of the HM⋯π interaction on the H⋯H interaction for the ternary system with HNa or HK, while it is contrary in the ternary complex with HLi. Furthermore, the moderate cooperativity effects between the H⋯H and HM⋯π interactions exist in the ternary complexes with FH, while the remarkable cooperativity effects are present in those with the partially covalent ClH⋯HM or BrH⋯HM dihydrogen-bonding interaction. Cooperativity effects follow the order of XH⋯HNa⋯C6H6 > XH⋯HLi⋯C6H6 > XH⋯HK⋯C6H6 and ClH⋯HM⋯C6H6 > BrH⋯HM⋯C6H6 > FH⋯HM⋯C6H6. Cooperativity effect was analyzed using the surface electrostatic potentials, electron density shifts and AIM (Atoms in Molecules) methods as well as charges of the hydrogen atoms in H⋯H moiety. Although the same optimized geometry is obtained, the cooperativity energy obtained considering that it comes either from “X−⋯H2⋯M+⋯C6H6” or “XH⋯HM⋯C6H6” is different.