Theoretical studies on the halogen-bonding interactions of 2,5-dihydrofuran,2,5-dihydro-thiophene and XF（X=F,Cl,Br） were investigated at the MP2/aug-cc-pVDZ level.Results show that both n-type and π-type halogen-bonded complexes can be formed between C4H6O,C4H6S and XF.For C4H6O…XF（n）,C4H6O…XF（π） and C4H6S…XF（π）,the interaction energies,electron densities at the halogen bond critical point,and the charge transfer amount from donor to acceptor are all in sequence of B…F2B…ClFB…BrF（B=C4H6O and C4H6S）.The halogen-bonding interactions of C4H6O…BrF（n）,C4H6O…BrF（π）,C4H6S…F2（n）,C4H6S…ClF（n）,C4H6S…BrF（n） and C4H6S…BrF（π） are stronger,with bond character between covalent and ionic.The other halogen-bonding interactions are weaker,with bond character ＂closed-shell＂ electrostatic interactions.%运用MP2/aug-cc-pVDZ方法对2,5-二氢呋喃,2,5-二氢噻吩与XF（X=F,Cl,Br）之间的卤键作用进行了理论研究.研究发现：C4H6O,C4H6S与XF之间不仅存在O（S）…XF n型卤键,C=C双键与XF分子亦可形成π型卤键;对于C4H6O与XF之间的n型和π型卤键以及C4H6S与XF之间的π型卤键,卤键键能ΔE、键鞍点处的电子密度ρ（rc）以及电子给体到受体之间的电子转移数Δq（XF）均按B…F2〈B…ClF〈B…BrF（B=C4H6O,C4H6S）的顺序依次增大;对于卤键键能较大的体系C4H6O…BrF（n）,C4H6O…BrF（π）,C4H6S…F2（n）,C4H6S…ClF（n）,C4H6S…BrF（n）,C4H6S…BrF（π）,卤键作用介于离子键和共价键之间;而对于其它的卤键键能较小的体系,卤键作用为闭壳层静电作用.
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