X…Y(X=LiF,H3N,H2O; Y=HF,LiF)复合物中锂键、氢键的理论计算

在CCSD(T)/cc-pVTZ水平下，对X…Y(X=LiF,H3N,H2O; Y=HF, LiF)复合物的9个结构进行几何构型优化和红外振动频率计算. 根据定域化分子轨道、原子自然电荷、Wiberg键级的分析表明HFLiF分子中的H-F键是共价键, 而Li-F键则为离子键而非共价键. H3N…Y (Y=HF，LiF)、H2O…Y (Y=HF，LiF)中的氢键或锂键源于静电相互作用, 并非共用电子的共价键. 结合能的计算表明: 与HF相比, LiF与X (X=LiF, H2O, NH3)的结合能更高;结合能从高到低依次为 LiF > NH3 > H2O. 红外振动频率分析表明HF与NH3、H2O形成红移氢键,即 H-F键长增加, 相应的H-F伸缩振动频率降低. H3N…LiF的Li-F键键长增加同时伸缩振动频率减少. 而LiF与H2O形成锂键后，键长增加0.016 ?，而Li-F的伸缩振动频率反而增加了2 cm-1 , 即蓝移锂键.

Theoretical studies on hydrogen bond and lithium bond in X…Y(X=LiF,H3N,H2O; Y=HF,LiF) complexes

Nine structures of X…Y(X=LiF,H3N,H2O; Y=HF, LiF) complexes were optimized on CCSD(T)/cc-pVTZ level. The results of natural atomic charges, Wiberg bond index and localized molecular orbitals suggest that H-F bond in HFLiF is covalent bond, but Li-F bond is more like ionic bond instead of covalent bond. The bind energy of LiF with X (X=LiF, H2O, NH3) is higher than X…HF. The order of bind energy is LiF…Y> H3N…Y > H2O…Y (Y=LiF, HF). The obtained vibrational frequencies of H-F bond in H3N…HF or H2O…HF decrease while H-F bond length increase, suggesting red-shifting hydrogen bond. The red-shifting lithium bond is also found in H3N…LiF. In H2O…LiF, it is found that Li-F bond elongated 0.016 ? while the stretch vibrational frequency of Li-F increased 2 cm-1 . Thus, the lithium bond in H2O…LiF should be considered as blue-shifting lithium bond.