Zirconium(IV) chloride

Zirconium(IV) chloride, also known as zirconium tetrachloride, (ZrCl₄) is an inorganic compound frequently used as a precursor to other compounds of zirconium. This white high-melting solid hydrolyzes rapidly in humid air.

Zirconium(IV) chloride

Names
IUPAC names Zirconium tetrachloride Zirconium(IV) chloride
Identifiers
CAS Number	10026-11-6 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:77566 N
ChemSpider	23202 Y
ECHA InfoCard	100.030.041
EC Number	233-058-2
PubChem CID	24817
UNII	Z88176T871 N
CompTox Dashboard (EPA)	DTXSID1044142
InChI InChI=1S/4ClH.Zr/h4*1H;/q;;;;+4/p-4 Y Key: DUNKXUFBGCUVQW-UHFFFAOYSA-J Y InChI=1/4ClH.Zr/h4*1H;/q;;;;+4/p-4 Key: DUNKXUFBGCUVQW-XBHQNQODAQ
SMILES Cl[Zr](Cl)(Cl)Cl
Properties
Chemical formula	ZrCl4
Molar mass	233.04 g/mol
Appearance	white crystals
Density	2.80 g/cm3
Melting point	437 °C (819 °F; 710 K) (triple point)
Boiling point	331 °C (628 °F; 604 K) (sublimes)
Solubility in water	hydrolysis
Solubility	concentrated HCl (with reaction)
Structure
Crystal structure	Monoclinic, mP10
Space group	P12/c1, No. 13
Thermochemistry
Heat capacity (C)	125.38 J K−1 mol−1
Std molar entropy (S⦵298)	181.41 J K−1 mol−1
Std enthalpy of formation (ΔfH⦵298)	−980.52 kJ/mol
Hazards
GHS labelling:[1]
Pictograms
Signal word	Danger
Hazard statements	H290, H302, H312, H314, H317, H332, H334
Precautionary statements	P234, P260, P261, P264, P270, P271, P272, P280, P285, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P312, P304+P340, P304+P341, P305+P351+P338, P310, P312, P321, P322, P330, P333+P313, P342+P311, P363, P390, P404, P405, P501
NFPA 704 (fire diamond)	3 0 2 W
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1488-1500 mg/kg (oral, rat) 655 mg/kg (mouse, oral)[2]
Safety data sheet (SDS)	MSDS
Related compounds
Other anions	Zirconium(IV) fluoride Zirconium(IV) bromide Zirconium(IV) iodide
Other cations	Titanium tetrachloride Hafnium tetrachloride
Related compounds	Zirconium(II) chloride, Zirconium(III) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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: TiCl
₄ is distillable, but ZrCl
₄ 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 bases, which cleave the Zr-Cl-Zr linkages.^[4]

Synthesis

This conversion entails treatment of zirconium oxide with carbon in the presence of chlorine at high temperature:

ZrO₂ + 2 C + 2 Cl₂ → ZrCl₄ + 2 CO

A laboratory scale process uses carbon tetrachloride in place of carbon and chlorine:^[5]

ZrO₂ + 2 CCl₄ → ZrCl₄ + 2 COCl₂

Applications

Precursor to zirconium metal

ZrCl₄ is an intermediate in the conversion of zirconium minerals to metallic zirconium by the Kroll process. In nature, zirconium minerals usually 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 at high temperatures. The purified ZrCl₄ can be reduced with Zr metal to produce zirconium(III) chloride.

Other uses

ZrCl₄ is the most common precursor for chemical vapor deposition of zirconium dioxide and zirconium diboride.^[6]

In organic synthesis zirconium tetrachloride is used as a weak Lewis acid for the Friedel-Crafts reaction, the Diels-Alder reaction and intramolecular cyclisation reactions.^[7] It is also used to make water-repellent treatment of textiles and other fibrous materials.

Properties and reactions

Hydrolysis of ZrCl₄ gives the hydrated hydroxy chloride cluster called zirconyl chloride. This reaction is rapid and virtually irreversible, consistent with the high oxophilicity 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.^[8] Because of its polymeric structure, ZrCl₄ is usually converted to a molecular complex before use. It forms a 1:2 complex with tetrahydrofuran: CAS [21959-01-3], mp 175–177 °C.^[9] Sodium cyclopentadienide (NaC₅H₅) reacts with ZrCl₄(THF)₂ to give zirconocene dichloride, ZrCl₂(C₅H₅)₂, a versatile organozirconium complex.^[10] One of the most curious properties of ZrCl₄ is its high solubility in the presence of methylated benzenes, such as durene. This solubilization arises through the formation of π-complexes.^[11]

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 torrs and temperature in kelvins. 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.^[12]

References

1. GHS: PubChem
2. "Zirconium compounds (as Zr)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
3. "New Environment Inc. - NFPA Chemicals". newenv.com. Retrieved 26 April 2017.
4. N. N. Greenwood & A. Earnshaw, Chemistry of the Elements (2nd ed.), Butterworth-Heinemann, Oxford, 1997.
5. Hummers, W. S.; Tyree, S. Y.; Yolles, S. (1953). "Zirconium and Hafnium Tetrachlorides". Inorganic Syntheses. Vol. IV. McGraw-Hill Book Company, Inc. p. 121. doi:10.1002/9780470132357.ch41. ISBN 978-0-470-13235-7.
6. Randich, E. (1 November 1979). "Chemical vapor deposited borides of the form (Ti,Zr)B₂ and (Ta,Ti)B₂". Thin Solid Films. 63 (2): 309–313. Bibcode:1979TSF....63..309R. doi:10.1016/0040-6090(79)90034-8.
7. Bora U. (2003). "Zirconium Tetrachloride". Synlett (7): 1073–1074. doi:10.1055/s-2003-39323.
8. Ilan Marek, ed. (2005). New Aspects of Zirconium Containing Organic Compounds. Topics in Organometallic Chemistry. Vol. 10. Springer: Berlin, Heidelberg, New York. doi:10.1007/b80198. ISBN 978-3-540-22221-7. ISSN 1436-6002.
9. L. E. Manzer; Joe Deaton (1982). "31. Tetragtdrfuran Complexes of Selected Early Transition Metals". Inorganic Syntheses. Vol. 21. pp. 135–140. doi:10.1002/9780470132524.ch31. ISBN 978-0-470-13252-4.
10. Wilkinson, G.; Birmingham, J. G. (1954). "Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta". J. Am. Chem. Soc. 76 (17): 4281–4284. doi:10.1021/ja01646a008.
11. Musso, F.; Solari, E.; Floriani, C.; Schenk, K. (1997). "Hydrocarbon Activation with Metal Halides: Zirconium Tetrachloride Catalyzing the Jacobsen Reaction and Assisting the Trimerization of Alkynes via the Formation of η⁶-Arene-Zirconium(IV) Complexes". Organometallics. 16 (22): 4889–4895. doi:10.1021/om970438g.
12. Palko, A. A.; Ryon, A. D.; Kuhn, D. W. (March 1958). "The Vapor Pressures of Zirconium Tetrachloride and Hafnium Tetrachloride". J. Phys. Chem. 62 (3): 319–322. doi:10.1021/j150561a017. hdl:2027/mdp.39015086513051.