Actinium(III) fluoride

Actinium(III) fluoride (AcF₃) is an inorganic compound, a salt of actinium and fluorine.

Actinium fluoride can be prepared in solution or by a solid-state reaction. In the first method, actinium hydroxide is treated with hydrofluoric acid and the product precipitates:

In the solid-state reaction, actinium metal is treated with hydrogen fluoride gas at 700 °C in a platinum crucible.

Actinium fluoride is a white solid that reacts with ammonia at 900–1000 °C to yield an actinium oxyfluoride:

While lanthanum oxyfluoride is easily formed by heating lanthanum fluoride in air, a similar treatment merely melts actinium fluoride and does not yield AcOF.