复合物TEMPO…XY中自由基卤键的性质及协同效应

Nature of Radical Halogen Bond in the TEMPO…XY Complexes and Its Cooperativity

采用量子化学计算方法,研究了2,2,6,6四甲基哌啶1氧自由基(TEMPO)与卤化物XY(X=Cl,Br,I;Y=CH_(3),CF_(3),CN)间的自由基卤键的结构与性质及卤键间的协同效应.复合物TEMPO…XY中的自由基卤键为较弱的闭壳层非共价作用.当Y相同时,卤键强度按照X=Cl,Br,I的顺序依次增强;当X相同时,随着取代基CH_(3),CF_(3),CN吸电子能力的增强,卤键作用逐渐增强.卤键的结合能与卤原子σhole处的静电势值、O…X键鞍点处电子密度、能量密度值及分子间积分电荷存在良好的线性关系.与双分子复合物中的卤键相比,三分子复合物NCX…TEMPO…XCN中O…X卤键作用减弱,卤键之间存在负协同效应;TEMPO…XCN…XCN复合物中O…X和N…X卤键彼此加强,具有正协同效应.

Quantumn chemical calculations have been performed to investigate the structure and nature of radical halogen bond and its cooperative effect between 2,2,6,6-tetramethylpiperidine 1-oxygen radical(TEMPO)and halides XY(X=Cl,Br,I;Y=CH_(3),CF_(3),CN).The halogen bonds in the TEMPO…XY complexes show the.character of weak closed noncovalent interactionsFor the same Y,the strength of halogen bond increases with the.order of X=Cl,Br,I.For the same X,the strength of halogen bond becomes larger with the increase of electron-withdrawing ability of the substituents CH_(3),CF_(3),CN.There are good linear relationships between binding energies and the most positive molecular electrostatic potential values on the σ-hole region,electron density and enegy density at the O…X BCPs,the quantity of integral charge in the intermolecular region.In the trimolecular complexes NCX…TEMPO…XCN(X=Cl,Br,I),the strength of O…X) halogen bond is weaker than that in the.corresponding bimolecular complexes,showing the negative synergistic effect between these halogen bonds.In the TEMPO…XCN…XCN complexes,O…X halogen bond and N…X halogen bond reinforce each other,and have a positive synergistic effect.