SOLVATION OF HALIDE-IONS WITH CH3OH IN THE GAS-PHASE

The gas-phase solvation reactions, X- (CH3OH)n-1 + CH3OH half-arrow-right-over-half-arrow-left X- (CH3OH)n, for X- = F-, Br-, and I-, were studied using a pulsed electron beam high pressure mass spectrometer. The - DELTA-G-degrees-n-1.n values are in the order F- > Cl- > Br- > I-. However, the - DELTA-H-degrees-n-1.n values for Br- and I- decrease more gradually with n than those for F- and Cl- and they follow the order F- > I- > Br- > Cl- with n greater-than-or-equal-to 6. The first solvation shells of X- (CH3OH)n for X- = F-, Cl-, and Br- seem to be completed with six CH3OH ligands. The - DELTA-H-degrees-n-1.n values for I- are almost independent of n and the completion of the first solvation shell does not take place up until n = 8. Owing to crowding in the inner shell, the - DELTA-S-degrees-n-1.n values for I- increase steadily with n. The differences between the cumulative thermochemical values, DELTA-G-degrees-0.n, DELTA-H-degrees-0.n, and T-DELTA-S-degrees-0.n, do not approach the differential thermochemical values for solution.