The Crucial Role of Sb₂ F₁₀ in the Chemical Synthesis of F₂

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 F₂ . This apparent discrepancy has now been resolved experimentally and by electronic structure calculations. It is shown that the reductive elimination of F₂ requires a large excess of SbF₅ and occurs in the last reaction step when in the intermediate [SbF₆ ][MnF₂ ][Sb₂ F₁₁ ] the addition of one more SbF₅ molecule to the [SbF₆ ]^- anion generates a second tridentate [Sb₂ F₁₁ ]^- anion. The two tridentate [Sb₂ F₁₁ ]^- anions then provide six fluorine bridges to the Mn atom thereby facilitating the reductive elimination of the two fluorine ligands as F₂ .