Hafnium tetrachloride

Last updated
Hafnium(IV) chloride
Zirconium-tetrachloride-3D-balls-A.png
Names
IUPAC names
Hafnium(IV) chloride
Hafnium tetrachloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.033.463 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/4ClH.Hf/h4*1H;/q;;;;+4/p-4 Yes check.svgY
    Key: PDPJQWYGJJBYLF-UHFFFAOYSA-J Yes check.svgY
  • InChI=1/4ClH.Hf/h4*1H;/q;;;;+4/p-4
    Key: PDPJQWYGJJBYLF-XBHQNQODAR
  • Cl[Hf](Cl)(Cl)Cl
Properties
HfCl4
Molar mass 320.302 g/mol
Appearancewhite crystalline solid
Density 3.89 g/cm3 [1]
Melting point 432 °C (810 °F; 705 K)
decomposes [2]
Vapor pressure 1 mmHg at 190 °C
Structure
Monoclinic, mP10 [1]
C2/c, No. 13
a = 0.6327 nm, b = 0.7377 nm, c = 0.62 nm
4
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
irritant and corrosive
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
2362 mg/kg (rat, oral) [3]
Safety data sheet (SDS) MSDS
Related compounds
Other anions
Hafnium tetrafluoride
Hafnium(IV) bromide
Hafnium(IV) iodide
Other cations
Titanium(IV) chloride
Zirconium(IV) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.

Contents

Preparation

HfCl4 can be produced by several related procedures:

HfO2 + 2 CCl4 → HfCl4 + 2 COCl2
HfO2 + 2 Cl2 + C → HfCl4 + CO2

Separation of Zr and Hf

Hafnium and zirconium occur together in minerals such as zircon, cyrtolite and baddeleyite. Zircon contains 0.05% to 2.0% hafnium dioxide HfO2, cyrtolite with 5.5% to 17% HfO2 and baddeleyite contains 1.0 to 1.8 percent HfO2. [9] Hafnium and zirconium compounds are extracted from ores together and converted to a mixture of the tetrachlorides.

The separation of HfCl4 and ZrCl4 is difficult because the compounds of Hf and Zr have very similar chemical and physical properties. Their atomic radii are similar: the atomic radius is 156.4 pm for hafnium, whereas that of Zr is 160 pm. [10] These two metals undergo similar reactions and form similar coordination complexes.

A number of processes have been proposed to purify HfCl4 from ZrCl4 including fractional distillation, fractional precipitation, fractional crystallization and ion exchange. The log (base 10) of the vapor pressure of solid hafnium chloride (from 476 to 681 K) is given by the equation: log10P = −5197/T + 11.712, where the pressure is measured in torrs and temperature in kelvins. (The pressure at the melting point is 23,000 torrs.) [11]

One method is based on the difference in the reducibility between the two tetrahalides. [9] The tetrahalides can in be separated by selectively reducing the zirconium compound to one or more lower halides or even zirconium. The hafnium tetrachloride remains substantially unchanged during the reduction and may be recovered readily from the zirconium subhalides. Hafnium tetrachloride is volatile and can therefore easily be separated from the involatile zirconium trihalide.

Structure and bonding

This group 4 halide contains hafnium in the +4 oxidation state. Solid HfCl4 is a polymer with octahedral Hf centers. Of the six chloride ligands surrounding each Hf centre, two chloride ligands are terminal and four bridge to another Hf centre. In the gas phase, both ZrCl4 and HfCl4 adopt the monomeric tetrahedral structure seen for TiCl4. [12] Electronographic investigations of HfCl4 in gas phase showed that the Hf-Cl internuclear distance is 2.33 Å and the Cl...Cl internuclear distance is 3.80 Å. The ratio of intenuclear distances r(Me-Cl)/r(Cl...Cl) is 1.630 and this value agrees well with the value for the regular tetrahedron model (1.633). [10]

Reactivity

Structure of HfCl4(thf)2. VEHZAJ.svg
Structure of HfCl4(thf)2.

The compound hydrolyzes, evolving hydrogen chloride:

HfCl4 + H2O → HfOCl2 + 2 HCl

Aged samples thus often are contaminated with oxychlorides, which are also colourless.

THF forms a monomeric 2:1 complex: [14]

HfCl4 + 2 OC4H8 → HfCl4(OC4H8)2

Because this complex is soluble in organic solvents, it is a useful reagent for preparing other complexes of hafnium.

HfCl4 undergoes salt metathesis with Grignard reagents. In this way, tetrabenzylhafnium can be prepared.

4 C6H5CH2MgCl + HfCl4 → (C6H5CH2)4Hf + 4 MgCl2

Similarly, salt metathesis with sodium cyclopentadienide gives hafnocene dichloride:

2 NaC5H5 + HfCl4 → (C5H5)2HfCl2 + 2 NaCl

With alcohols, alkoxides are formed.

HfCl4 + 4 ROH → Hf(OR)4 + 4 HCl

These compounds adopt complicated structures.

Reduction

Reduction of HfCl4 is especially difficult. In the presence of phosphine ligands, reduction can be effected with potassium-sodium alloy: [15]

2 HfCl4 + 2 K + 4 P(C2H5)3 → Hf2Cl6[P(C2H5)3]4 + 2 KCl

The deep green dihafnium product is diamagnetic. X-ray crystallography shows that the complex adopts an edge-shared bioctahedral structure, very similar to the Zr analogue.

Uses

Hafnium tetrachloride is the precursor to highly active catalysts for the Ziegler-Natta polymerization of alkenes, especially propylene. [16] Typical catalysts are derived from tetrabenzylhafnium.

HfCl4 is an effective Lewis acid for various applications in organic synthesis. For example, ferrocene is alkylated with allyldimethylchlorosilane more efficiently using hafnium chloride relative to aluminium trichloride. The greater size of Hf may diminish HfCl4's tendency to complex to ferrocene. [17]

HfCl4 increases the rate and control of 1,3-dipolar cycloadditions. [18] It was found to yield better results than other Lewis acids when used with aryl and aliphatic aldoximes, allowing specific exo-isomer formation.

Microelectronics applications

HfCl4 was considered as a precursor for chemical vapor deposition and atomic layer deposition of hafnium dioxide and hafnium silicate, used as high-k dielectrics in manufacture of modern high-density integrated circuits. [19] However, due to its relatively low volatility and corrosive byproducts (namely, HCl), HfCl4 was phased out by metal-organic precursors, such as tetrakis ethylmethylamino hafnium (TEMAH). [20]

Related Research Articles

<span class="mw-page-title-main">Zirconium</span> Chemical element, symbol Zr and atomic number 40

Zirconium is a chemical element with the symbol Zr and atomic number 40. The name zirconium is derived from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian zargun. It is a lustrous, grey-white, strong transition metal that closely resembles hafnium and, to a lesser extent, titanium. Zirconium is mainly used as a refractory and opacifier, although small amounts are used as an alloying agent for its strong resistance to corrosion. Zirconium forms a variety of inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. Five isotopes occur naturally, four of which are stable. Zirconium compounds have no known biological role.

A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:

Silane (Silicane) is an inorganic compound with chemical formula SiH4. It is a colourless, pyrophoric, toxic gas with a sharp, repulsive, pungent smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Silane with alkyl groups are effective water repellents for mineral surfaces such as concrete and masonry. Silanes with both organic and inorganic attachments are used as coupling agents. Silanes are commonly used to apply coatings to surfaces or as an adhesion promoter.

<span class="mw-page-title-main">Titanium tetrachloride</span> Inorganic chemical compound

Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4" due to the phonetic resemblance of its molecular formula to the word.

<span class="mw-page-title-main">Iron(II) chloride</span> Chemical compound

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions.

<span class="mw-page-title-main">Zirconium(IV) chloride</span> Chemical compound

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

Titanium(III) chloride is the inorganic compound with the formula TiCl3. At least four distinct species have this formula; additionally hydrated derivatives are known. TiCl3 is one of the most common halides of titanium and is an important catalyst for the manufacture of polyolefins.

Zirconium(IV) bromide is the inorganic compound with the formula ZrBr4. This colourless solid is the principal precursor to other Zr–Br compounds.

Technetium compounds are chemical compounds containing the chemical element technetium. Technetium can form multiple oxidation states, but often forms in the +4 and +7 oxidation states. Because technetium is radioactive, technetium compounds are extremely rare on Earth.

<span class="mw-page-title-main">Organozirconium and organohafnium chemistry</span>

Organozirconium chemistry is the science of exploring the properties, structure, and reactivity of organozirconium compounds, which are organometallic compounds containing chemical bonds between carbon and zirconium. Organozirconium compounds have been widely studied, in part because they are useful catalysts in Ziegler-Natta polymerization.

<span class="mw-page-title-main">Germanium dichloride</span> Chemical compound

Germanium dichloride is a chemical compound of germanium and chlorine with the formula GeCl2. It is a yellow solid. Germanium dichloride is an example of a compound featuring germanium in the +2 oxidation state.

<span class="mw-page-title-main">Zirconium(III) chloride</span> Chemical compound

Zirconium(III) chloride is an inorganic compound with formula ZrCl3. It is a blue-black solid that is highly sensitive to air.

In organometallic chemistry, bent metallocenes are a subset of metallocenes. In bent metallocenes, the ring systems coordinated to the metal are not parallel, but are tilted at an angle. A common example of a bent metallocene is Cp2TiCl2. Several reagents and much research is based on bent metallocenes.

<span class="mw-page-title-main">Titanium ethoxide</span> Chemical compound

Titanium ethoxide is a chemical compound with the formula Ti4(OCH2CH3)16. It is a commercially available colorless liquid that is soluble in organic solvents but hydrolyzes readily. Alkoxides of titanium(IV) and zirconium(IV) are used in organic synthesis and materials science. They adopt more complex structures than suggested by their empirical formulas.

<span class="mw-page-title-main">Metal halides</span>

Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric structures, such as palladium chloride.

<span class="mw-page-title-main">Lead(IV) chloride</span> Chemical compound

Lead tetrachloride, also known as lead(IV) chloride, has the molecular formula PbCl4. It is a yellow, oily liquid which is stable below 0 °C, and decomposes at 50 °C. It has a tetrahedral configuration, with lead as the central atom. The Pb–Cl covalent bonds have been measured to be 247 pm and the bond energy is 243 kJ⋅mol−1.

<span class="mw-page-title-main">Hafnocene dichloride</span> Chemical compound

Hafnocene dichloride is the organohafnium compound with the formula (C5H5)2HfCl2. It is a white solid that is sparingly soluble in some organic solvents. The lighter homologues zirconacene dichloride and titanocene dichloride have received much more attention. While hafnocene is only of academic interest, some more soluble derivatives are precatalysts for olefin polymerization. Moreso than the Zr analogue, this compound is highly resistant to reduction.

<span class="mw-page-title-main">Protactinium(IV) chloride</span> Chemical compound

Protactinium(IV) chloride is an inorganic compound. It is an actinide halide, composed of protactinium and chlorine. It is radioactive, and has the chemical formula of PaCl4. It is a chartreuse-coloured (yellowish-green) crystal of the tetragonal crystal system.

Hafnium compounds are compounds containing the element hafnium (Hf). Due to the lanthanide contraction, the ionic radius of hafnium(IV) (0.78 ångström) is almost the same as that of zirconium(IV) (0.79 angstroms). Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties. Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides. At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Some compounds of hafnium in lower oxidation states are known.

References

  1. 1 2 Niewa R., Jacobs H. (1995) Z. Kristallogr.210: 687
  2. ↑ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.66. ISBN   1-4398-5511-0.
  3. ↑ "Hafnium compounds (as Hf)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. ↑ Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 11 (4th ed.). 1991.
  5. ↑ Hummers, W. S.; Tyree, Jr., S. Y.; Yolles, S. (1953). Zirconium and Hafnium Tetrachlorides. Inorganic Syntheses. Vol. 4. p. 121. doi:10.1002/9780470132357.ch41. ISBN   9780470132357.
  6. ↑ Hopkins, B. S. (1939). "13 Hafnium". Chapters in the chemistry of less familiar elements. Stipes Publishing. p. 7.
  7. ↑ Hála, Jiri (1989). Halides, oxyhalides and salts of halogen complexes of titanium, zirconium, hafnium, vanadium, niobium and tantalum. Vol. 40 (1st ed.). Oxford: Pergamon. pp. 176–177. ISBN   978-0080362397.
  8. ↑ Elinson, S. V. and Petrov, K. I. (1969) Analytical Chemistry of the Elements: Zirconium and Hafnium. 11.
  9. 1 2 Newnham, Ivan Edgar "Purification of Hafnium Tetrachloride". U.S. Patent 2,961,293 November 22, 1960.
  10. 1 2 Spiridonov, V. P.; Akishin, P. A.; Tsirel'Nikov, V. I. (1962). "Electronographic investigation of the structure of zirconium and hafnium tetrachloride molecules in the gas phase". Journal of Structural Chemistry. 3 (3): 311. doi:10.1007/BF01151485. S2CID   94835858.
  11. ↑ Palko, A. A.; Ryon, A. D.; Kuhn, D. W. (1958). "The Vapor Pressures of Zirconium Tetrachloride and Hafnium Tetrachloride". The Journal of Physical Chemistry. 62 (3): 319. doi:10.1021/j150561a017. hdl: 2027/mdp.39015086446302 .
  12. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 964–966. ISBN   978-0-08-037941-8.
  13. ↑ Duraj, S. A.; Towns; Baker; Schupp, J. (1990). "Structure of cis-Tetrachlorobis(tetrahydrofuran)hafnium(IV)". Acta Crystallographica . C46 (5): 890–2. doi: 10.1107/S010827018901382X .
  14. ↑ Manzer, L. E. (1982). "Tetrahydrofuran Complexes of Selected Early Transition Metals". Inorg. Synth. 21: 135–140. doi:10.1002/9780470132524.ch31. ISBN   978-0-470-13252-4.
  15. ↑ Riehl, M. E.; Wilson, S. R.; Girolami, G. S. (1993). "Synthesis, X-ray Crystal Structure, and Phosphine-Exchange Reactions of the Hafnium(III)-Hafnium(III) Dimer Hf2Cl6[P(C2H5)3]4". Inorg. Chem. 32 (2): 218–222. doi:10.1021/ic00054a017.
  16. ↑ Ron Dagani (2003-04-07). "Combinatorial Materials: Finding Catalysts Faster". Chemical and Engineering News . p. 10.
  17. ↑ Ahn, S.; Song, Y. S.; Yoo, B. R.; Jung, I. N. (2000). "Lewis Acid-Catalyzed Friedel−Crafts Alkylation of Ferrocene with Allylchlorosilanes". Organometallics. 19 (14): 2777. doi:10.1021/om0000865.
  18. ↑ Graham, A. B.; Grigg, R.; Dunn, P. J.; Higginson, P. (2000). "Tandem 1,3-azaprotiocyclotransfer–cycloaddition reactions between aldoximes and divinyl ketone. Remarkable rate enhancement and control of cycloaddition regiochemistry by hafnium(iv) chloride". Chemical Communications (20): 2035–2036. doi:10.1039/b005389i.
  19. ↑ Choi, J. H.; Mao, Y.; Chang, J. P. (2011). "Development of hafnium based high-k materials—A review". Materials Science and Engineering: R: Reports. 72 (6): 97. doi:10.1016/j.mser.2010.12.001.
  20. ↑ Robertson, John (2006). "High dielectric constant gate oxides for metal oxide Si transistors". Reports on Progress in Physics . 69 (2): 327–396. Bibcode:2006RPPh...69..327R. doi:10.1088/0034-4885/69/2/R02. S2CID   122044323.
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