The interplay and the formation of σ-hole in the π···LiX and pseudo-π···LiX (X = F, Cl and CN) lithium bonds involving unsaturated and homocyclic hydrocarbons

[Display omitted] •The lithium bond strength was revisited.•The blue-shifts and red-shifts in the Li-bonds was revealed by means of the analyses of the infrared spectra.•The conformation of the σ-hole was demonstrated through the occupancy of the p-orbital of Li-atom.•The blue-shifts are manifested in the strongly bound complexes.•The exchange repulsion agrees totally with the blue-shifts and the σ-hole. A theoretical study at the level of the density functional theory and ab initio correlation calculations was carried out in order to better understand the intermolecular properties of π∙∙∙Li and pseudo-π∙∙∙Li interactions formed between the C2H2, C2H4 or C3H6 and LiX (X = F, Cl and CN). The extremely high values of the lithium bond energies followed by red-shifts and blue-shifts are the cornerstone of these systems, although the magnitude of the σ-hole in the Li–X bond agrees with the interaction strength profile. The atomic charge on the Li-atom had to be also analyzed because this parameter is mandatory to assure the lithium bond formation. Ideally, the σ-hole is predicted by variations in the occupancy of the p-orbitals of the F, Cl or C elements. Lastly, the energy decomposition analyses provided a suitable explanation for the frequency shifts to red or blue according to exchange energy calculation.