Hexafluorophosphoric acid refers to a family of salts produced by combining phosphorus pentafluoride and hydrofluoric acid. The idealized chemical formula for hexafluorophosphoric acid
is HPF6, which also is written H[PF]6.[3] Hexafluorophosphoric acid is only stable in solution, decomposing to HF and PF5 when dry.[4] It exothermically reacts with water to produce oxonium hexafluorophosphate (H3OPF6) and hydrofluoric acid. Additionally, such solutions often contain products derived from hydrolysis of the P-F bonds, including HPO 2F 2, H 2PO 2F, and H 3PO 4, and their conjugate bases.[5] Hexafluorophosphoric acid attacks glass. Upon heating, it decomposes to generate HF. Crystalline HPF 6 has been obtained as the hexahydrate, wherein PF− 6 is enclosed in truncated octahedral cages defined by the water and protons. NMR spectroscopy indicates that solutions derived from this hexahydrate contain significant amounts of HF.[5]
Whereas a species with the formula HPF6 remains unknown, the analogous molecular hexafluoroarsenic acid (HAsF6) has been crystallized.[6]
^Axhausen, Joachim; Lux, Karin; Kornath, Andreas (2014). "The Existence of Hexafluoroarsenic(V) Acid". Angewandte Chemie International Edition. 53 (14): 3720–3721. doi:10.1002/anie.201308023. PMID24446235.