PF6

PF6 commonly denotes the hexafluorophosphate ion, PF6−, or its salts. In this ion, phosphorus is in the +5 oxidation state and is surrounded by six fluorine ligands in an octahedral arrangement. The PF6− anion is a classic example of a weakly coordinating, non-nucleophilic counterion that provides electrostatic stabilization without strong direct bonding to cations.

Preparation and occurrence: Hexafluorophosphoric acid HPF6 is a typical precursor for PF6− salts. Anion exchange or metathesis reactions with various cations (such as Na+, K+, or bulky tetraalkylammonium ions) afford MF6 salts. PF6− is also encountered as part of lithium hexafluorophosphate LiPF6, a widely used electrolyte salt in lithium-ion batteries.

Properties and stability: PF6− is moisture sensitive and hydrolyzes in water, releasing HF and producing phosphate-oxyfluoride species; consequently PF6− salts are stored dry. The anion’s lack of coordinating ability makes it suitable for stabilizing highly reactive cations and for use in catalysis and crystallography.

Applications: It serves as a stable, non-coordinating counteranion in inorganic and organometallic chemistry, enabling isolation of cationic complexes. It is used in ionic liquids and as part of battery electrolytes (e.g., LiPF6).

Safety: PF6− salts can be corrosive; hydrofluoric acid release upon hydrolysis poses health hazards. Handle with appropriate protective equipment and keep away from moisture and incompatibles.