Tungsten Oxyfluorides

The oxyfluoride, WOF₄, has been prepared by interaction of the oxychloride, WOCl₄, with anhydrous hydrogen fluoride, and by heating tungsten trioxide with lead fluoride, bismuth fluoride, or cryolite. It forms small hygroscopic plates which are decomposed by water; it has the property also of absorbing in the cold half a molecule of ammonia, thereby becoming orange in colour.

Attempts to prepare the fluoride WO₂F₂ by similar methods were unsuccessful, though small quantities are formed by the action of water on the oxytetrafluoride; double compounds of the formulae 2KF.WO₂F₂.H₂O, KF.WO₂F.H₂O, 2TlF.WO₂F₂, 3TlF.2WO₂F₂, and TlF.WO₂F₂ have, however, been prepared. The complex salt, luteocobaltic fluoroxytungstate, Co(NH₃)₆F₃.2WO₂F₂, may be obtained by adding luteocobaltic fluoride to a solution of tungstic acid in hydrofluoric acid, and allowing to crystallise from the dilute acid solution. The crystals are stable at 110° C.