Theoretical study of the interplay between lithium bond and hydrogen bond in complexes involved with HLi and HCN.

The lithium- and hydrogen-bonded complex of HLi-NCH-NCH is studied with ab initio calculations. The optimized structure, vibrational frequencies, and binding energy are calculated at the MP2 level with 6-311++G(2d,2p) basis set. The interplay between lithium bonding and hydrogen bonding in the complex is investigated with these properties. The effect of lithium bonding on the properties of hydrogen bonding is larger than that of hydrogen bonding on the properties of lithium bonding. In the trimer, the binding energies are increased by about 19% and 61% for the lithium and hydrogen bonds, respectively. A big cooperative energy (-5.50 kcal mol(-1)) is observed in the complex. Both the charge transfer and induction effect due to the electrostatic interaction are responsible for the cooperativity in the trimer. The effect of HCN chain length on the lithium bonding has been considered. The natural bond orbital and atoms in molecules analyses indicate that the electrostatic force plays a main role in the lithium bonding. A many-body interaction analysis has also been performed for HLi-(NCH)(N) (N=2-5) systems.