Solvation of the Li+–Cl−–Li+ triple ion in the gas phase

Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry was employed to study solvations of the ${\mathrm{Li}}^{\mathrm{+}}{\mathrm{–Cl}}^{\mathrm{-}}{\mathrm{–Li}}^{\mathrm{+}}$ triple ion with oxygen-donor Lewis bases in the gas phase. The ${\mathrm{LiClLi}}^{\mathrm{+}}$ triple ions were produced in an ICR cell by laser desorption ionization of a lithium chloride/dibenzo-18-crown-6-ether matrix pasted on a Teflon substrate. O-donor Lewis bases include 1,4-dioxane, 1,3-dioxane, tetrahydrofuran (THF), acetone and diethyl ether. All O-donors associate directly with ${\mathrm{LiClLi}}^{\mathrm{+}}$ with the maximum solvation numbers of 3 for 1,4-dioxane, 1,3-dioxane and diethyl ether, and 4 for THF and acetone at room temperature. The rate constants for the stepwise solvations were measured, and the solvent binding energies were determined from van’t Hoff plots. The structures and energetics of ${\mathrm{LiClLi}}^{\mathrm{+}}$ and the 1:1 complexes of ${\mathrm{Li}}^{\mathrm{+}}$ and ${\mathrm{LiClLi}}^{\mathrm{+}}$ with the dioxanes, THF, and acetone were calculated at the Hartree-Fock (HF) level with a $\text{6-311}\mathrm{G}\mathrm{(d,p)}$ basis set, and those of more highly coordinated ${\mathrm{LiClLi}}^{\mathrm{+}}$ complexes were calculated with a $\text{6-31}\mathrm{G}\mathrm{(d)}$ basis set. Solvation enthalpies and free energies were calculated, and solvent binding energies were compared with experiments. The mechanisms of stepwise solvations of the ${\mathrm{LiClLi}}^{\mathrm{+}}$ triple ion with dioxanes, THF, and acetone are discussed in light of experimental kinetics and binding energies and theoretical structures and solvation energies.