Characterizing Complexes with F−Li⁺−F Lithium Bonds: Structures, Binding Energies, and Spin−Spin Coupling Constants

Ab initio MP2/aug-cc-pVTZ calculations have been performed to determine the structures and binding energies of complexes with F−Li⁺−F bonds formed from the fluorine bases LiF, CH₃F, HF, ClF, and FF. There is only a single minimum across the Li⁺ transfer coordinate, and in each series, the lithiated homodimer is stabilized by a symmetric F···Li⁺···F bond. Complexes having LiF, CH₃F, and HF as the base have similar structures, with linear F−Li⁺−F bonds and a head-to-tail alignment of the F−Li⁺ bond dipole with the dipole moment vector of the base. In each series with a given acid, the binding energy decreases as the difference between the lithium ion affinities increases. EOM-CCSD coupling constants ¹J(F−Li), ^1liJ(Li−F), and ^2liJ(F−F) have also been evaluated. In complexes with essentially linear bonds, ^2liJ(F−F) values are small and positive and increase quadratically as the F−F distance decreases. ^1liJ(Li−F) and ¹J(F−Li) also vary systematically with distance. Comparisons are made between structural, energetic, and coupling constant properties of these complexes and corresponding complexes stabilized by F−H⁺−F hydrogen bonds.