Ditopic Binding of Alkali Halide Ions to Trimethylboroxine

摘要

Trimethylboroxine (TMB) is a six-membered ring compound containing Lewis acidic boron and Lewis basic oxygen atoms that can bind halide anion and alkali metal cation, respectively. We employed Fourier transform ion cyclotron resonance spectroscopy to study the gas-phase binding of and to TMB. TMB forms association complexes with both and at room temperature, providing direct evidence for the ditopic binding. Interestingly, the anion complex is formed 33 times faster than the cation complex. To gain insight into the ditopic binding of an ion pair, we examined the structures and energetics of , , (the contact ion pair), and (the separated ion pair) using Hartree-Fock and density functional theory. Theory suggests that binds more strongly to TMB than and the contact ion-pair binding ( ) is more stable than the separated ion-pair binding ( ).