During an interesting discussion in our group’s seminar, the question arose what actually causes trifluoroacetic acid to be a much better nucleophile than trifluoromethanesulfonic acid. Part of the discussion was whether the oxygens of trifluoromethanesulfonic acid were equal or not.
Traditionally, $\ce{TfOH}$ is drawn as shown in the structure below on the left. The structure would assume the molecule having point group $C_\mathrm{s}$ due to the non-equality of the oxygen atoms only one of which bears a hydrogen. The triflate anion $\ce{TfO-}$ in solution, on the other hand, has three homotopic oxygens as can be seen in the structure on the right, leading to the more symmetric point group $C_\mathrm{3v}$.
One of the opinions voiced in the discussion was that even the gas-phase molecule $\ce{TfOH}$ adopted a $C_\mathrm{3v}$ point group, the hydrogen being in the same axis as carbon and sulfur and somewhat centred between the three oxygens. This makes perfect sense when thinking about it. Therefore, my questions are:
Has the structure of trifluoromethanesulfonic acid or a structurally strongly related acid been studied in the gas phase? (Please provide a reference)
Does the experiment suggest equivalent or non-equivalent oxygens?
How well can that idea be extended? e.g. should one consider the structure of formic acid to be $C_\mathrm{2v}$ symmetric rather than $C_\mathrm{s}$?
Do (solid-state) crystal structures or other experiments exist that confirm a different structure for solid $\ce{TfOH}$?
If solid and gas phase structures differ substantially, what about the structure of the molecule in liquid phase/solution?
