Computational Study of Complexation in <scp>LiH</scp>:<scp>nNH₃</scp> (<i>n</i> = 1–4) Clusters: An Interplay Among Hydrogen, Dihydrogen, and Lithium Bonds

Ab initio and density functional theory (DFT) calculations are employed to investigate LiH:nNH₃ (n = 1-4) cluster complexes. The nature of the interactions is analyzed using molecular electrostatic potential maps, quantum theory of atoms in molecules, delocalization indices, and electron density difference maps. In the presence of LiH, NH₃ molecules engage in several types of noncovalent interactions, namely, hydrogen bonding (HB), lithium bonding (LB), and dihydrogen bonding (DHB). The LiH:NH₃ dimer is stabilized primarily through Li···N interactions. The role of these noncovalent interactions in complexes having more than one NH₃ molecule, for example, hetero-trimer, tetramer, and pentamer structures, is also examined. Increasing the number of NH₃ molecules enhances the number of HB sites. Additionally, the strengths of LB and DHB interactions associated with HB-bonded NH₃ molecules increase. Interaction energy estimates and many-body energy decomposition analysis suggest that increasing NH₃ molecules increases cooperativity, approaching ~10% of the total interaction's energy in the case of tetramers and pentamers.