Hafnium tetrachloride
| Hafnium tetrachloride | |
|---|---|
| Hafnium(IV) chloride.jpg | |
| General | |
| Systematic name | Hafnium(IV) chloride Hafnium tetrachloride |
| Molecular formula | HfCl4 |
| Molar mass | 320.30 g/mol |
| Appearance | white crystalline solid |
| CAS number | [13499-05-3] |
| Properties | |
| phase | Solid |
| Solubility in water | decomposes |
| Melting point | 432 °C (705 K) |
| Structure | |
| Coordination geometry |
? |
| Crystal structure | presumed monoclinic |
| Hazards | |
| MSDS | MSDS |
| Main hazards | irritant and corrosive |
| NFPA 704 | Template:Nfpa |
| Flash point | non-flammable |
| Supplementary data | |
| Structure and properties |
n, εr, etc. |
| Themodynamics | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Other anions | Hafnium(IV) fluoride Hafnium(IV) bromide Hafnium(IV) iodide |
| Other cations | Titanium(IV) chloride Zirconium(IV) chloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
Hafnium(IV) chloride is a Group 4 metallic halide with the formula HfCl4. It contains hafnium in the +4 oxidation state. HfCl4 is precursor species used to form many hafnium organometallic compounds. It functions as a Lewis acid and catalyst for certain alkylation and isomerism reactions.
Preparation
HfCl4 is produced by several procedures. Chlorine and hafnium metal can form HfCl4 above 317 °C. Carbon tetrachloride and hafnium oxide can form HfCl4 at temperatures above 450 °C. Chlorine gas can be passed over a mixture of HfO2 and charcoal at temperatures above 600 °C to form HfCl4. Also, hafnium carbide can form HfCl4 when placed in a dry stream of Cl2 above 250 °C. None of these preparations are favored over the others.
Composition and structure
All geometric and crystal structures have not been established for hafnium halides. HfCl4 is not a molecular species; it is a polymer with chlorine ligand bridging. Since it shares many properties with ZrCl4, one can assume it may have structural similarities. ZrCl4 forms monoclinic crystals signaling that HfCl4 might as well. In vapor phase, both ZrCl4 and HfCl4 are expected to look like TiCl4 with monomeric tetrahedral structure.
As with all hafnium compounds, the most common contaminant is zirconium, here ZrCl4. This contamination occurs because Zr and Hf are found together in almost all sources.
Uses
HfCl4 is a Lewis acid and can act as a catalyst. It can also form other hafnium compounds. Illustrative applications are listed below.
- Formation of THF complexes in high yield
THF metal halide complexes have been difficult to produce in high yield. The complex is useful in organometallic syntheis.
- HfCl4 + 2 OC4H8 → HfCl4(OC4H8)2
- Formation of Hf(III) dimers
Little is known about Hf(III) compounds. HfCl4 is especially difficult to reduce, making the success of this reaction notable.
- HfCl4 + 2 Na/K + 4 P(C2H5)3 → Hf2Cl4[P(C2H5)3]4 + 2 (Na/K)Cl
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