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Zirconium(IV) chloride, also known as zirconium tetrachloride, () is an
inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
frequently used as a precursor to other compounds of zirconium. This white high-melting solid hydrolyzes rapidly in humid air.


Structure

Unlike molecular TiCl4, solid ZrCl4 adopts a polymeric structure wherein each Zr is octahedrally coordinated. This difference in structures is responsible for the disparity in their properties: is distillable, but is a solid. In the solid state, ZrCl4 adopts a tape-like linear polymeric structure—the same structure adopted by HfCl4. This polymer degrades readily upon treatment with
Lewis base A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
s, which cleave the Zr-Cl-Zr linkages.


Synthesis

This conversion entails treatment of the oxide with carbon as the oxide "getter" in the presence of chlorine at high temperature: :ZrO2 + 2 C + 2 Cl2 → ZrCl4 + 2 CO A laboratory scale process uses
carbon tetrachloride Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also IUPAC nomenclature of inorganic chemistry, recognised by the IUPAC, carbon tet in the cleaning industry, Halon-104 in firefighting, and Refrigerant-10 in HVAC ...
in place of carbon and chlorine: :ZrO2 + 2 CCl4 → ZrCl4 + 2 COCl2


Applications


Precursor to Zr metal

ZrCl4 is an intermediate in the conversion of zirconium minerals to metallic
zirconium Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'', ...
by the Kroll process. In nature, zirconium minerals invariably exist as oxides (reflected also by the tendency of all zirconium chlorides to hydrolyze). For their conversion to bulk metal, these refractory oxides are first converted to the tetrachloride, which can be
distilled Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heating ...
at high temperatures. The purified ZrCl4 can be reduced with Zr metal to produce
zirconium(III) chloride Zirconium(III) chloride is an inorganic compound with formula ZrCl3. It is a blue-black solid that is highly sensitive to air. Preparation The material was first claimed by Ruff and Wallstein who reduced zirconium tetrachloride with aluminium ...
.


Other uses

ZrCl4 is the most common precursor for
chemical vapor deposition Chemical vapor deposition (CVD) is a vacuum deposition method used to produce high quality, and high-performance, solid materials. The process is often used in the semiconductor industry to produce thin films. In typical CVD, the wafer (substra ...
of
zirconium dioxide Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabi ...
and zirconium diboride. In organic synthesis zirconium tetrachloride is used as a weak
Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
for the Friedel-Crafts reaction, the Diels-Alder reaction and intramolecular cyclisation reactions. It is also used to make water-repellent treatment of
textile Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...
s and other fibrous materials.


Properties and reactions

Hydrolysis of ZrCl4 gives the hydrated hydroxy chloride cluster called
zirconyl chloride Zirconyl chloride is the inorganic compound with the formula of r4(OH)8(H2O)16l8(H2O)12, more commonly written ZrOCl2·8H2O, and referred to as zirconyl chloride octahydrate. It is a white solid and is the most common water-soluble derivative of ...
. This reaction is rapid and virtually irreversible, consistent with the high
oxophilicity Oxophilicity is the tendency of certain chemical compounds to form oxides by hydrolysis or abstraction of an oxygen atom from another molecule, often from organic compounds. The term is often used to describe metal centers, commonly the early trans ...
of zirconium(IV). For this reason, manipulations of ZrCl4 typically require air-free techniques. ZrCl4 is the principal starting compound for the synthesis of many organometallic complexes of zirconium. Because of its polymeric structure, ZrCl4 is usually converted to a molecular complex before use. It forms a 1:2 complex with
tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
: CAS 1959-01-3 mp 175–177 °C.
Sodium cyclopentadienide Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pi ...
(NaC5H5) reacts with ZrCl4(THF)2 to give zirconocene dichloride, ZrCl2(C5H5)2, a versatile organozirconium complex. One of the most curious properties of ZrCl4 is its high solubility in the presence of methylated benzenes, such as
durene Durene, or 1,2,4,5-tetramethylbenzene, is an organic compound with the formula C6H2(CH3)4. It is a colourless solid with a sweet odor. The compound is classified as an alkylbenzene. It is one of three isomers of tetramethylbenzene, the other t ...
. This solubilization arises through the formation of π-complexes. The log (base 10) of the vapor pressure of zirconium tetrachloride (from 480 to 689 K) is given by the equation: log10(P) = −5400/T + 11.766, where the pressure is measured in
torr The torr (symbol: Torr) is a unit of pressure based on an absolute scale, defined as exactly of a standard atmosphere (). Thus one torr is exactly (≈ ). Historically, one torr was intended to be the same as one "millimeter of mercury ...
s and temperature in
kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...
s. The log (base 10) of the vapor pressure of solid zirconium tetrachloride (from 710 to 741 K) is given by the equation log10(P) = −3427/T + 9.088. The pressure at the melting point is 14,500 torrs.


References

{{Chlorides Zirconium(IV) compounds Chlorides Metal halides Coordination complexes