Tungsten(VI) fluoride, also known as tungsten hexafluoride, is an inorganic compound with the formula WF6. It is a toxic, corrosive, colorless gas, with a density of about (roughly 11 times heavier than air). It is one of the densest known gases under standard conditions. WF6 ls commonly used by the semiconductor industry to form tungsten films, through the process of chemical vapor deposition. This layer is used in a low-resistivity metallic "interconnect". It is one of seventeen known binary hexafluorides. Properties The WF6 molecule is octahedral with the symmetry point group of Oh. The W–F bond distances are . Between , tungsten hexafluoride condenses into a pale yellow liquid having the density of at . At it freezes into a white solid having a cubic crystalline structure, the lattice constant of 628 pm and calculated density . At this structure transforms into an orthorhombic solid with the lattice constants of , , and , and the density of . In this phase, the W–F distance is 181 pm, and the mean closest molecular contacts are . Whereas WF6 gas is one of the densest gases, with the density exceeding that of the heaviest elemental gas radon (9.73 g/L), the density of WF6 in the liquid and solid state is rather moderate. The vapor pressure of WF6 between can be described by the equation , where the P = vapor pressure (bar), T = temperature (°C). Synthesis Tungsten hexafluoride is commonly produced by the exothermic reaction of fluorine gas with tungsten powder at a temperature between : W + 3 F2 → WF6 The gaseous product is separated from WOF4, a common impurity, by distillation. In a variation on the direct fluorination, the metal is placed in a heated reactor, slightly pressurized to , with a constant flow of WF6 infused with a small amount of fluorine gas. The fluorine gas in the above method can be substituted by , or . An alternative procedure for producing tungsten fluoride is to react tungsten trioxide (WO3) with HF, BrF3 or SF4. Tungsten fluoride can also be obtained by conversion of tungsten hexachloride: WCl6 + 6 HF → WF6 + 6 HCl or WCl6 + 2 AsF3 → WF6 + 2 AsCl3 or WCl6 + 3 SbF5 → WF6 + 3 SbF3Cl2 Reactions On contact with water, tungsten hexafluoride gives hydrogen fluoride (HF) and tungsten oxyfluorides, eventually forming tungsten trioxide: WF6 + 3