第一主族阳离子-苯复合物相互作用的理论研究

运用从头算MP2和密度泛函B3LYP方法，在6-311＋＋G^＊＊基组水平上对第一主族阳离子-苯复合体系的构型进行了自由优化，并定义阳离子位于苯环正上方。频率计算表明为合理构型，复合物的键长、原子电荷、分子轨道成份、前沿轨道能等表明，碱金属阳离子与苯的作用包含p-π和s-π作用方式，阳离子与苯结合时电子从苯向阳离子转移，形成电荷转移复合物，与氢键的结合方式相似。M^＋…benzene and benzene…M^＋…benzene复合物的红外光谱特征频率分别位于120～740cm^-1和140-890cm^-1，为阳离子垂直于环平面上作来回振动，其红外光谱振动频率随Li、Na、K向长波方向红移，并红外强度随Li、Na、K降低。

Theoretical Study of Cation-π Interactions of Monovalent Cation H^＋, Li^＋, Na^＋, K^＋ with Benzene

Calculations on monovalent cations-benzene complexes were performed using the density-functional theory （DFT） B3LYP and ab initio MP2 methods with 6-311 ＋ ＋ G^＊＊ basis set, where the monovalent cations are located on the C6 axis above the benzene plane. The calculated IR spectrum show that the these structures are reasonable. The bond lengths, total atomic charge, the coefficients of the molecular orbitals, frontier orbital energies of the complexes indicate that the interaction between alkali metal cations and benzene involve p-π interaction and s-π interaction. On the other hand, electron is transferred from the benzene to the monovalent cations, and thus gives charge transfer complexes. The calculated results also imply that the interaction characteristic of the alkali metal cation-benzene complexes are similar to hydrogen bonding. The normal mode analysis of the predicted vibrational frequency shows that the characteristic vibration mode of the complex is located at 120-740cm^-1 and 140 890cm^-1 , which corresponds to the down and up vibration of the alkali metal cations above the benzene ring plane respectively, and on the vibrational frequency of the M^＋… benzene and benzene… M^＋ …benzene with potassium, sodium and lithium, which IR intensity weskening with potassium, sodium and lithium.