Potassium Thorifluoride, K₂ThF₆.4H₂O

Potassium Thorifluoride, K₂ThF₆.4H₂O, is formed as an amorphous, insoluble powder when freshly precipitated thorium hydroxide is boiled with a concentrated solution of potassium fluoride containing hydrofluoric acid. The precipitate obtained by adding thorium chloride to potassium hydrogen fluoride solution is possibly KTh₂F₉.6H₂O, whilst with neutral potassium fluoride the product is KThF₅.H₂O. When thorium fluoride and potassium fluoride are fused together and the mass is extracted with water KThF₅ remains; and when acidified rubidium fluoride is added to a thorium salt solution RbThF₅.3H₂O is precipitated. The amorphous and insoluble natures of these compounds differentiate them from other double or complex fluorides of the fourth group.