Characteristic Changes of Bond Energies for Gas-Phase Cluster Ions of Halide Ions with Methane and Chloromethanes

Gas-phase equilibria for clustering reactions of both halide ions (X - ) with methane and chloride ions with chloromethanes (CH 4 - m Cl m ) were measured with a pulsed electron-beam high-pressure mass spectrometer. The bond energies were found to show irregular decreases for F - (CH 4 ) n, with n = 6 and 8, for Cl - (CH 3 Cl) n, with n = 2, 4, and 6, and for Cl - (CH 2 Cl 2 ) n, with n = 2 and 4. These even numbers indicate that the core ions are preferably solvated by the ligands with these n values. The theoretical calculation revealed that the cluster ion Cl - (CCl 4 ) has the structure of [Cl...ClCCl 3 ] - rather than Cl - ...Cl 3 CCl. The unexpectedly large bond energy for Cl - (CCl 4 ) (13.4 kcal/mol) is due to the charge dispersal in the complex [Cl...ClCCl 3 ] - .