Tantalum(V) chloride
Chemical compound
From Wikipedia, the free encyclopedia
Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder, which is highly sensitive to moisture. It is synthesised and manipulated under anhydrous conditions, using air-free techniques.[2][3]
Tantalum, Ta; Chlorine, Cl | |
| Names | |
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| IUPAC names
Tantalum(V) chloride Tantalum pentachloride | |
| Identifiers | |
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3D model (JSmol) |
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| ChemSpider | |
| ECHA InfoCard | 100.028.869 |
| EC Number |
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PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| TaCl5 | |
| Molar mass | 358.213 g/mol |
| Appearance | white monoclinic crystals[1][page needed][contradictory] |
| Density | 3.68 g/cm3 |
| Melting point | 216 °C (421 °F; 489 K) |
| Boiling point | 239.4 °C (462.9 °F; 512.5 K) (decomposes) |
| reacts | |
| Solubility | chloroform, CCl4 |
| +140.0×10−6 cm3/mol | |
| Structure | |
| Monoclinic, mS72 | |
| C2/m, No. 12 | |
| Thermochemistry | |
Std molar entropy (S⦵298) |
221.75 J K−1 mol−1 |
Std enthalpy of formation (ΔfH⦵298) |
−858.98 kJ/mol |
| Hazards | |
| GHS labelling: | |
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| Danger | |
| H302, H314, H335 | |
| P260, P264+P265, P270, P271, P280, P301+P317, P301+P330+P331, P302+P361+P354, P304+P340, P305+P351+P338, P305+P354+P338, P310, P316, P330, P363, P403+P233, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
1900 mg/kg (oral, rat) |
| Safety data sheet (SDS) | External SDS |
| Related compounds | |
Other anions |
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Other cations |
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Related compounds |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure
TaCl5 crystallizes in the monoclinic space group C2/m.[4] The ten chlorine atoms define a pair of octahedra that share a common edge. The tantalum atoms occupy the centres of the octahedra and are joined by two chlorine bridging ligands. The dimeric structure Ta2Cl10 is retained in non-complexing solvents and to a large extent in the molten state. In the vapour state, however, TaCl5 is monomeric. This monomer adopts a trigonal bipyramidal structure, like that of PCl5.[5][page needed]
Synthesis
Tantalum pentachloride can be prepared by treating powdered metallic tantalum with chlorine gas at between 170 and 250 °C. This reaction can also be performed using HCl at 400 °C.[6]
- 2 Ta + 5 Cl2 → 2 TaCl5
- 2 Ta + 10 HCl → 2 TaCl5 + 5 H2
It can also be prepared by a reaction between tantalum pentoxide and thionyl chloride at 240 °C.[3]
- Ta2O5 + 5 SOCl2 → 2 TaCl5 + 5 SO2
Tantalum pentachloride is commercially available, however samples can be contaminated with tantalum(V) oxytrichloride (TaOCl3), formed by hydrolysis. Samples contaminated with niobium pentachloride appear yellow.[3]
Reactions
TaCl5 is electrophilic. It forms adducts with a variety of Lewis bases. It serves as a Lewis acid in Friedel-Crafts reactions.[7]
Simple adducts
TaCl5 forms stable complexes with ethers:.[7][8]
TaCl5 also reacts with phosphorus pentachloride and phosphoryl chloride, the former as a chloride donor and the latter serves as a ligand, binding through the oxygen:[9]
- TaCl5 + PCl5 → [PCl4]+[TaCl6]−
- TaCl5 + OPCl3 → [TaCl5(OPCl3)]
Tantalum pentachloride reacts with tertiary amines to give adducts:[7]
- TaCl5 + 2 R3N → [TaCl5(NR3)]
Chloride displacement reactions
Tantalum pentachloride reacts at room temperature with an excess of triphenylphosphine oxide to give oxychlorides:
- TaCl5 + 3 OPPh3 → [TaOCl3(OPPh3)]x ...
Hydrolysis, alcoholysis, ammonolysis and related reactions
Anhydrous TaCl5 (Ta2Cl10) rapidly (but not violently) hydrolyses in water at room temperature.[10]
Tantalum pentachloride reacts with sodium ethoxide to give the pentaethoxide, which also exists as a dimer:[11]
- 5 NaOC2H5 + TaCl5 → Ta(OC2H5)5 + NaCl
A variety of related alkoxides and mixed chloro-alkoxides are known, e.g. Ta(OCH3)5 and Ta(OCH2CH3)3Cl2.[7]
Ammonium chloride gives the nitrido complex [TaCl5N]3−.[12]
Reduction
Reduction of tantalum(V) chloride gives anionic and neutral clusters including [Ta6Cl18]4− and [Ta6Cl14](H2O)4.[13]
