heptafluorodiphosphate

Heptafluorodiphosphate is an inorganic anion with the chemical formula P2F7-. It consists of two phosphorus atoms linked by a single bond, with fluorine atoms surrounding them. The structure is often described as two PF4 groups joined by a P-P bond, with one fluorine atom bridging the two phosphorus atoms, leading to a pentagonal bipyramidal coordination around each phosphorus, though this representation can be misleading. More accurately, it can be viewed as two PF3 groups bonded to a central F2P-PF2 unit, with additional fluorine atoms completing the coordination spheres.

Heptafluorodiphosphate is typically encountered as a salt, for instance, potassium heptafluorodiphosphate (K2P2F7). These salts are often formed from the reaction of alkali metal fluorides with phosphorus pentafluoride (PF5) or related compounds. It is a relatively stable species under normal conditions, though it can decompose at elevated temperatures. The P-P bond is generally considered to be the weakest bond within the molecule.

The heptafluorodiphosphate anion is a component of certain ionic liquids and has been investigated for applications in electrochemistry and as a component in non-aqueous electrolytes. Its chemical properties are influenced by the electronegativity of fluorine, leading to a highly polarized structure. It is important to distinguish heptafluorodiphosphate from other phosphorus-fluorine compounds like hexafluorophosphate (PF6-) or tetrafluoroborate (BF4-).