Does HF prefer to be attached to X or M of XHHM (X = F, Cl, Br; M = Li, Na, K) system? A B3LYP and MP2 theoretical investigation into cooperativity effect

The cooperativity effects are investigated in the possible linear dihydrogen-bonded ternary complexes, F-H center dot center dot center dot X-H center dot center dot center dot H-M and X-H center dot center dot center dot H-M+center dot center dot center dot F-H, and non-dihydrogen-bonded quaternary systems, F-H center dot center dot center dot X-center dot center dot center dot H-H center dot center dot center dot M+ and X-center dot center dot center dot H-H center dot center dot center dot M+center dot center dot center dot F-H (X=F, Cl, Br; M=Li, Na, K) using the DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) methods. The result shows that for the dihydrogen-bonded complex, remarkable cooperativity effect is found and the cooperativity effect of the H center dot center dot center dot H bond on the H center dot center dot center dot X or M center dot center dot center dot F interaction is more pronounced than that of the H center dot center dot center dot X or M center dot center dot center dot F contact on the H center dot center dot center dot H interaction. The complexation energy and cooperativity effect in F-H center dot center dot center dot X-H center dot center dot center dot H-M are larger than those of the corresponding X-H center dot center dot center dot H-M center dot center dot center dot F-H system. Thus, the FH center dot center dot center dot XH center dot center dot center dot HM complex is preferentially formed and F-H prefers to be attached to the X end. For the non-dihydrogen-bonded quaternary system, due to the stronger complexation energy and cooperativity effect of Cl-center dot center dot center dot H-H center dot center dot center dot Li+center dot center dot center dot F-H or F-H center dot center dot center dot Br-center dot center dot center dot H-H center dot center dot center dot K+ as compared to those of F-H center dot center dot center dot Cl-center dot center dot center dot H-H center dot center dot center dot Li+ or Br-center dot center dot center dot H-H center dot center dot center dot K+center dot center dot center dot F-H, F-H prefers to be attached to Li+ or Br-. Cooperativity effect is analyzed using the charges on hydrogen in the H center dot center dot center dot H moiety, surface electrostatic potentials and atoms in molecules analysis.