The Crucial Role of Sb2F10 in the Chemical Synthesis of F-2

The purely chemical synthesis of fluorine is a spectacular reaction which for more than a century had been believed to be impossible. In 1986, it was finally experimentally achieved, but since then this important reaction has not been further studied and its detailed mechanism had been a mystery. The known thermal stability of MnF4 casts serious doubts on the originally proposed hypothesis that MnF4 is thermodynamically unstable and decomposes spontaneously to a lower manganese fluoride and F-2. This apparent discrepancy has now been resolved experimentally and by electronic structure calculations. It is shown that the reductive elimination of F-2 requires a large excess of SbF5 and occurs in the last reaction step when in the intermediate [SbF6][MnF2][Sb2F11] the addition of one more SbF5 molecule to the [SbF6](-) anion generates a second tridentate [Sb2F11](-) anion. The two tridentate [Sb2F11](-) anions then provide six fluorine bridges to the Mn atom thereby facilitating the reductive elimination of the two fluorine ligands as F-2.