Nature Of Halogen Bonds In Solution

The halogen bond(XB)occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another,or the same molecular entity.Due to its high directionality and tunable strength,halogen bond exists generally on self-assemble materials,recognition processes and drug synthesis,and gains more and more attentions from chemists.In this paper,the nature of two-center neutral halogen bonds in solvent environments is investigated by generalized Kohn-Sham energy decomposition analysis(GKS-EDA).It's found that when solvent environment is simulated by implicit solvation model,the simple difference of the solvation free energy,which neglects the BSSE and the cavity superposition error,may be not appropriate for the description of halogen bond in solution,while GKS-EDA has the capability of considering the two errors together,providing a reasonable interpretation of the variation of halogen bonds from gas phase to solvent environments.It's also found that in both gas phase and aqueous solution,halogen bond is dominated by electrostatic interaction.Polarization interaction responses for their behaviors in solution.If polarization is large,the total binding energy is sensitive to solvent environments.Halogen bond becomes large with the polar solvent effect.If polarization is relatively small,close to dispersion and correlation term,the variation of total binding energy is small.With the hard and soft acids and bases(HSAB)theory,the larger the monomer softness of the halogen bond,the greater the corresponding polarization,the more obvious the solvent effect on the halogen bond;The smaller the degree of softness,the smaller the corresponding polarization,the less sensitive the halogen bond to the solvent effect.In addition,varying pattern of ionization potential were studied on hydrogen bond systems formed by 9HFCA(9-hydroxyl-9-fluorene-carboxylic acid)and a series of small molecules(simple inorganic acids and bases like NH3,H2O,HCl;small carboxylic acid and its derivatives).It's found that the ionization potential of hydrogen bond systems is dominated by polarization interaction.For the hydrogen bonds between 9HFCA and carboxylic acids or its derivatives,the varying pattern of ionization potential of hydrogen bond was found.The ionization potential can be regulated through the substitution on the-CH3 of acetic acid.With the substituted group becoming more and more electron-withdrawing,the ionization potential of the hydrogen bond system tends to be blue shift.With the substituted group becoming more and more electron-donating,the ionization potential of the hydrogen bond system tends to be blue shift.