With this in mind, we sought to increase the relative concentration of fluoride (with respect to Ca 2+ ) by employing TMAF in THF instead of benzene. Therefore, a solution of 4 in THF was added dropwise to a pre-sonicated and rapidly stirred THF-solution of TMAF (2.0 equiv.). Under these conditions a single (different) fluorine-containing species was observed, giving rise to a signal at F = -82.1 ppm. The downfield shift in the F signal (compared to those measured for compounds 6-8) is of the same sense as that observed between single and doubly fluoridebridged NON-ligated calcium fluoride complexes (e.g. F = -87.3 and -70.