Niobium(V) chloride

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.[1]

Niobium(V) chloride
Names
IUPAC names
Niobium(V) chloride
Niobium pentachloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.042
EC Number
  • 233-059-8
RTECS number
  • QU0350000
UNII
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 HCl, chloroform, CCl4
Thermochemistry
214.05 JK−1mol−1
-797.47 kJ/mol
Hazards
GHS pictograms
GHS Signal word Danger
H302, H312, H314, H332
P260, P261, P264, P270, P271, P280, P301+312, P301+330+331, P302+352, P303+361+353, P304+312, P304+340, P305+351+338, P310, P312, P321, P322, P330, P363, P405, P501
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).
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Infobox references

Structure and properties

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.[2] NbBr5, TaCl5 and TaBr5 are isostructural with NbCl5, but NbI5 and TaI5 have different structures.

Preparation

Industrially, niobium pentachloride is obtained by direct chlorination of niobium metal at 300 to 350 °C:[3]

2 Nb + 5 Cl2 → 2 NbCl5

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:[4] 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.

Uses

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.[5]

References

  1. Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, ISBN 0-471-02775-8
  2. Cotton, F.A., P. A. Kibala, M. Matusz and R. B. W. Sandor (1991). "Structure of the Second Polymorph of Niobium Pentachloride". Acta Crystallogr. C. 47 (11): 2435–2437. doi:10.1107/S0108270191000239.CS1 maint: multiple names: authors list (link)
  3. Joachim Eckert, Hermann C. Starck (2005). "Niobium and Niobium Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_251.CS1 maint: uses authors parameter (link)
  4. D. Brown "Niobium(V) Chloride and Hexachloroniobates(V)" Inorganic Syntheses, 1957 Volume 9, pp. 88–92.doi:10.1002/9780470132401.ch24
  5. Andrade, C. K. Z.; Rocha, R. O.; Russowsky, D. & Godoy, M. N. (2005). "Studies on the Niobium Pentachloride-Mediated Nucleophilic Additions to an Enantiopure Cyclic N-acyliminium Ion Derived from (S)-malic acid" (PDF). J. Braz. Chem. Soc. 16 (3b): 535–539. doi:10.1590/S0103-50532005000400007. Archived from the original (PDF) on 2007-10-12.
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