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∙∙∙X–H∙∙∙H–M and X–H∙∙∙H–M∙∙∙F–H, and non-dihydrogen-bonded quaternary systems, F–H∙∙∙X–∙∙∙H–H∙∙∙M+ and X–∙∙∙H–H∙∙∙M+∙∙∙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∙∙∙H bond on the H∙∙∙X or M∙∙∙F interaction is more pronounced than that of the H∙∙∙X or M∙∙∙F contact on the H∙∙∙H interaction. The complexation energy and cooperativity effect in F–H∙∙∙X–H∙∙∙H–M are larger than those of the corresponding X–H∙∙∙H–M∙∙∙F–H system. Thus, the F–H∙∙∙X–H∙∙∙H–M 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–∙∙∙H–H∙∙∙Li+∙∙∙F–H or F–H∙∙∙Br–∙∙∙H–H∙∙∙K+ as compared to those of F–H∙∙∙Cl–∙∙∙H–H∙∙∙Li+ or Br–∙∙∙H–H∙∙∙K+∙∙∙F–H, F–H prefers to be attached to Li+ or Br–. Cooperativity effect is analyzed using the charges on hydrogen in the H∙∙∙H moiety, surface electrostatic potentials and atoms in molecules analysis.
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