Tungsten(VI) Fluoride

Introduction

Name: Tungsten(VI) Fluoride
Other Names: Tungsten Hexafluoride; Tungsten Fluoride
CAS: 7783-82-6
GB Number: 23025
GB Number: WF₆
GB Number: 297.8
Boiling Point: 17.5℃
Melting Point: 2.3℃
Hazard Markers:6(Toxic Gases)

Nature

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is the inorganic compound of tungsten and fluorine with the formula WF₆. This corrosive, colorless compound is a gas under standard conditions, with a density of about 13g/L (roughly 11 times heavier than air.), WF₆ is one of the heaviest known gases under standard conditions. WF₆ gas is most commonly used in the production of semiconductor circuits and circuit boards through the process of chemical vapor deposition – upon decomposition, molecules of WF₆ leave a residue of metallic tungsten. This layer serves as low-resistive metallic "interconnect".

At ambient pressure and temperatures above 17°C, tungsten hexafluoride is a colorless diamagnetic gas. The WF₆ molecule is octahedral with the symmetry point group of Oh. The W–F bond distances are 183.2 pm. Between 2.3 and 17°C, tungsten hexafluoride condenses into a pale yellow liquid having the density of 3.44 g/cm3 at 15 °C. At 2.3 °C it freezes into a white solid having a cubic crystalline structure, the lattice constant of 628 pm and calculated density 3.99 g/cm3. At −9 °C this structure transforms into an orthorhombic solid with the lattice constants of a = 960.3 pm, b = 871.3 pm, and c = 504.4 pm, and the density of 4.56 g/cm3. In this phase, the W–F distance is 181 pm, and the mean closest intermolecular contacts are 312 pm. Whereas WF6 gas is one of the heaviest 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 −70 °C and 17 °C can be described by the equation.

Tungsten hexafluoride is a colorless gas or pale yellow liquid, its solid is a deliquescent white crystal which smokes in the moist air. Tungsten hexafluoride is a colorless, transparent liquid or gas odorless at different temperatures, the molecule has a symmetrical octahedron structure at room temperature. The relative density of tungsten hexafluoride is 3.44 (water=1) (15 ℃), it can soluble in most organic solvents, react with hydrofluoric acid to generate [H₂ [WF₈].
Tungsten hexafluoride is a strong fluorinating agent, which can fluoridate many metal except for nickel, Monel and stainless steel at room temperature; has weak corrosion to glass in the dry condition, but takes out reaction quickly in the moisture.
Tungsten hexafluoride and ionic halide coordination compounds can be formed, and can be reduced to hydrogen tungsten at high temperatures. Tungsten hexafluoride will quickly hydrolyzed in the water, to generate hydrogen fluoride (HF) and tungsten trioxide, thus the toxicity of tungsten hexafluoride is substantially the same to HF in the air.

Application

Tungsten hexafluoride is mainly used for chemical vapor deposition of tungsten, and also used as a fluorinating agent.