On the structure and stability of gas-phase cluster ions SiF3+(CO)n, SiF3OH2+(SiF4)n, SiF4H+(SiF4)n, and F-(SiF4)n

Gas-phase ion/molecule reactions in SiF4 were measured using a pulsed-electron beam mass spectrometer. The thermochemical stabilities of SiF3+(CO)(n), SiF3OH2+(SiF4)(n), SiF4H+(SiF4)(n), and F-(SiF4)(n) have been studied experimentally and theoretically. Owing to the serious charging of the ion source, only up to n = 2 thermochemical data could be obtained experimentally. The bond energy for SiF3+... CO of 41.6 kcal/mol is found to be much larger than that for CF3+... CO of. 16.0 kcal/mol. This indicates that SiF3+ is a much stronger Lewis acid than CF3+. The SiF3+(CO)(2) cluster has the D-3h structure, OC ... SiF3+... CO, which is the core for the larger cluster ions, [SiF3(CO)(2)](+)(CO)(n-2). In the cluster ion SiF4H+(SiF4)(2), a C-2 symmetry structure, (F-3-SiF ... F-H-F ... SiF3)(+), has been obtained. In the cluster F-(SiF4)(2), the F- ion is sandwiched by the two SiF4 molecules equivalently, indicating the charge dispersal in the complex.