Nine structures of X… Y (X =LiF,NH3,H2 O;Y =HF,LiF) complexes were optimized at CCSD (T)/ccpVTZ level.The results of natural atomic charges,Wiberg bond index and localized molecular orbitals suggest that H-F bond in HFLiF is covalent,but Li-F bond is more like ionic instead of covalent.The bind energy of LiF with X (X =LiF,H2O,NH3) is higher than that of 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 a 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 0.001 6 nm 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.%在CCSD(T)/cc-pVTZ水平下,对X…Y(X=LiF、NH3、H2O;Y=HF、Lir)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0.0016 nm,而Li-F的伸缩振动频率反而增加了2 cm-1,即蓝移锂键.
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