Hafnium tetrachloride
Names | |
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IUPAC names
Hafnium(IV) chloride
Hafnium tetrachloride | |
Identifiers | |
3D model (
JSmol ) |
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ChemSpider | |
ECHA InfoCard
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100.033.463 |
PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
HfCl4 | |
Molar mass | 320.302 g/mol |
Appearance | white 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 | |
C2/c, No. 13 | |
a = 0.6327 nm, b = 0.7377 nm, c = 0.62 nm
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4 | |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards
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irritant and corrosive |
Flash point | Non-flammable |
Lethal dose or concentration (LD, LC): | |
LD50 (median dose)
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2362 mg/kg (rat, oral)[3] |
Safety data sheet (SDS) | MSDS |
Related compounds | |
Other anions
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Hafnium(IV) bromide
Hafnium(IV) iodide |
Other cations
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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).
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Hafnium(IV) chloride is the
Preparation
HfCl4 can be produced by several related procedures:
- The reaction of
- HfO2 + 2 CCl4 → HfCl4 + 2 COCl2
- Chlorination of a mixture of HfO2 and
- HfO2 + 2 Cl2 + C → HfCl4 + CO2
- Chlorination of hafnium carbide above 250 °C.[8]
Separation of Zr and Hf
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: log10 P = −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
The compound hydrolyzes, evolving hydrogen chloride:
- HfCl4 + H2O → HfOCl2 + 2 HCl
Aged samples thus often are contaminated with oxychlorides, which are also colourless.
- 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
- 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
- 2 HfCl4 + 2 K + 4 P(C2H5)3 → Hf2Cl6[P(C2H5)3]4 + 2 KCl
The deep green dihafnium product is
Uses
Hafnium tetrachloride is the precursor to highly active catalysts for the
HfCl4 is an effective Lewis acid for various applications in
HfCl4 increases the rate and control of 1,3-dipolar cycloadditions.
Microelectronics applications
HfCl4 was considered as a precursor for
References
- ^ a b Niewa R., Jacobs H. (1995) Z. Kristallogr. 210: 687
- ISBN 1-4398-5511-0.
- ^ "Hafnium compounds (as Hf)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ^ Kirk-Othmer Encyclopedia of Chemical Technology. Vol. 11 (4th ed.). 1991.
- ISBN 9780470132357.
- ^ Hopkins, B. S. (1939). "13 Hafnium". Chapters in the chemistry of less familiar elements. Stipes Publishing. p. 7.
- ISBN 978-0080362397.
- ^ Elinson, S. V. and Petrov, K. I. (1969) Analytical Chemistry of the Elements: Zirconium and Hafnium. 11.
- ^ a b Newnham, Ivan Edgar "Purification of Hafnium Tetrachloride". U.S. patent 2,961,293 November 22, 1960.
- ^ S2CID 94835858.
- .
- ISBN 978-0-08-037941-8.
- .
- ISBN 978-0-470-13252-4.
- .
- Chemical and Engineering News. p. 10.
- .
- doi:10.1039/b005389i.
- .
- S2CID 122044323.