Mutual influence between conventional and unconventional lithium bonds

The interplay between conventional and unconventional lithium bonds interactions in NCLi⋯NCLi⋯XCCX and CNLi⋯CNLi⋯XCCX (X=H, F, Cl, Br, OH, CH3, and OCH3) complexes is studied by ab initio calculations. Cooperative effects are observed when Li⋯N(C) and Li⋯π bonds coexist in the same complex. These effects are analyzed in terms of geometric, energetic and electron charge density properties of the complexes. The cooperative effects are larger in those complexes with shorter intermolecular distances than in those with the longest ones. The electron density at the lithium bond critical points can be regarded as a good descriptor of the degree of cooperative effects. An excellent linear correlation can be obtained between the cooperative energies and the calculated spin-spin coupling constants across the lithium bonds.