苯-卤素(X_2,X=F,Cl,Br,I)相互作用本质的对称性匹配微扰理论研究

Symmetry-adapted Perturbation Theory Study on the Nature of Benzene-halogen(X_2,X=F,Cl,Br,I)

在MP2水平下对被定义为"电荷转移复合物(CTC)"的苯(C6H6)-卤素分子X2(X=F,Cl,Br,I)相互作用体系进行了量子化学研究.在优化所得C6H6-X2(X=F,Cl,Br,I)复合物的平衡几何结构中,卤素分子X2接近垂直指向苯环上碳-碳双键的中心.自然键轨道(NBO)分析结果表明,苯-卤素体系中电荷转移的数量很少.对称性匹配微扰理论(Symmetry-adapted perturbation theory,SAPT)能量分解结果显示,在4个复合物体系中,静电作用的贡献相对较小(只占总吸引作用的20%左右),对于C6H6-F2体系,色散作用是其主要吸引作用,对于C6H6-Cl2,C6H6-Br2和C6H6-I2体系,诱导作用则是其主要的吸引作用,从F到I,色散作用逐渐减弱,诱导作用逐渐增强,表明在电子相关水平上将苯-卤素体系称为"电荷转移复合物"的说法并不确切.

A theoretical study of the charge-transfer complexes（CTC）,as defined by Mulliken,formed by benzene and dihalogen molecules X2（X=F,Cl,Br,I） was carried out with second-order Mller-Plesset perturbation（MP2）.In the global minimum of C6H6-X2（X= F,Cl,Br,I）,the halogen molecule is located above one of the C—C bond centers of benzene,and the halogen molecule bond axis also slightly tilts towards the axis perpendicular to the plane of the benzene ring.The natural bond orbital（NBO） analysis reveals that the number of charge-transfer is negligible for these charge-transfer complexes.Symmetry-adapted perturbation theory（SAPT） results show that the contribution of electrostatic effects to halogen bonding interactions is relatively small,and generally accounts for about 20% of the attractive interaction for the four complexes.Halogen bonding interaction in C6H6-F2 system is principally dispersive in nature.The halogen bonds containing chlorine,bromine and iodine are largely dependent on the induction type interactions.And,interestingly,more induction（and less dispersive） interaction appears from F to I.The so-called ＂charge-transfer complexes（CTC）＂ for C6H6-X2 system is not exact on electron correlation level.