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.