Actinium(III) fluoride (AcF<sub>3</sub>) 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 ðC in a platinum crucible.
Actinium fluoride is a white solid that reacts with ammonia at 900âÂÂ1000 ðC 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.