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Niobium pentachloride

Niobium(V) chloride
Sample of niobium(V) chloride
Niobium-pentachloride-dimer-2D.png
Names
IUPAC names
Niobium(V) chloride
Niobium pentachloride
Identifiers
10026-12-7 NbCl5 N
17499-28-4 Nb2Cl10 N
ECHA InfoCard 100.030.042
EC Number 233-059-8
PubChem 24818
RTECS number QU0350000
UNII 9S1BC7865F N
Properties
NbCl5
Molar mass 270.17 g/mol
Appearance yellow monoclinic crystals
deliquescent
Density 2.75 g/cm3
Melting point 204.7 °C (400.5 °F; 477.8 K)
Boiling point 248.2 °C (478.8 °F; 521.3 K)
decomposes
Solubility soluble in alcohol, HCl, chloroform, CCl4
Thermochemistry
214.05 J K−1 mol−1
-797.47 kJ/mol
Hazards
Flash point Non-flammable
Related compounds
Other anions
Niobium(V) fluoride
Niobium(V) bromide
Niobium(V) iodide
Other cations
Vanadium(IV) chloride
Tantalum(V) chloride
Related niobium chlorides
Niobium(III) chloride
Niobium(IV) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Niobium(V) chloride, also known as niobium pentachloride, is a yellow crystalline solid. It hydrolyzes in air, and samples are often contaminated with small amounts of NbOCl3. It is often used as a precursor to other compounds of niobium. NbCl5 may be purified by sublimation.

Niobium(V) chloride forms chloro-bridged dimers in the solid state (see figure). Each niobium centre is six-coordinate, but the octahedral coordination is significantly distorted. The equatorial niobium–chlorine bond lengths are 225 pm (terminal) and 256 pm (bridging), whilst the axial niobium-chlorine bonds are 229.2 pm and are deflected inwards to form an angle of 83.7° with the equatorial plane of the molecule. The Nb–Cl–Nb angle at the bridge is 101.3°. The Nb–Nb distance is 398.8 pm, too long for any metal-metal interaction. NbBr5, TaCl5 and TaBr5 are isostructural with NbCl5, but NbI5 and TaI5 have different structures.

Industrially, niobium pentachloride is obtained by direct chlorination of niobium metal at 300 to 350 °C:

In the laboratory, niobium pentachloride is often prepared from Nb2O5, the main problem being incomplete reaction to give the oxyhalides. The conversion can be effected with thionyl chloride: It also can be prepared by chlorination of niobium pentoxide in the presence of carbon at 300 °C. The products, however, contain small amounts of NbOCl3.

Niobium(V) chloride is the main precursor to the alkoxides of niobium, which find niche uses in sol-gel processing. It is also the precursor to many other laboratory reagents.

In organic synthesis, NbCl5 is a specialized Lewis acid in activating alkenes for the carbonyl-ene reaction and the Diels-Alder reaction. Niobium chloride can also generate N-acyliminium compounds from certain pyrrolidines which are substrates for nucleophiles such as allyltrimethylsilane, indole, or the silyl enol ether of benzophenone.


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