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Niobium(V) chloride
Sample of niobium(V) chloride
Niobium-pentachloride-dimer-2D.png
IUPAC name
Identifiers
CAS number 10026-12-7 Yes check.svgY
EC number 233-059-8
RTECS number QU0350000
Properties
Molecular formula NbCl5
Molar mass 270.17 g/mol
Appearance yellow monoclinic crystals
deliquescent
Density 2.75 g/cm3
Melting point

204.7 °C

Boiling point

248.2 °C

Solubility in water decomposes
Solubility soluble in alcohol, HCl, chloroform, CCl4
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-797.47 kJ/mol
Standard molar
entropy
So298
214.05 J K−1 mol−1
Hazards
EU Index Not listed
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
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Niobium(V) chloride, also known as niobium pentachloride, is a yellow crystalline solid often used as a starting material in niobium chemistry. It is prepared by heating niobium metal in chlorine. It is often contaminated with small amounts of niobium(V) oxychloride, NbOCl3, formed by hydrolysis or from traces of oxygen during the preparation. NbCl5 may be purified by sublimation.

Contents

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

Ball-and-stick model of niobium pentachloride

Preparation

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

2Nb + 5Cl2 → 2NbCl5

It also may be made by chlorination of niobium pentoxide in the presence of carbon at 300°C. The products, however, contain small amounts of niobium oxide trichloride, NbOCl3.

Uses

Niobium(V) chloride is used in organic chemistry as a 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.[2]

Recently, a work was presented for a new synthesis of nano-sized niobate oxyde particles by a low temperature three steps procedure.[3]. The complete protocol implies a LiH induced reduction of NbCl5 followed by in situ spontaneous oxidation into low valence niobium nano-oxides. These niobium oxides are exposed to air atmosphere leading to pure Nb2O5 formation.

Bibliography

References

  1. ^ Cotton, F.A., P. A. Kibala, M. Matusz and R. B. W. Sandor (1991). "Structure of the Second Polymorph of Niobium Pentachloride". Acta Cryst. C47: 2435–2437. doi:10.1107/S0108270191000239.  
  2. ^ 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". J. Braz. Chem. Soc. 16: 535–539. doi:10.1590/S0103-50532005000400007. http://jbcs.sbq.org.br/online/2005/vol16_n3B/06-144-04.pdf.  
  3. ^ Aufray M, Menuel S, Fort Y, Eschbach J, Rouxel D, Vincent B (2009). "New Synthesis of Nanosized Niobium Oxides and Lithium Niobate Particles and Their Characterization by XPS Analysis". JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 9 (8): 4780–4789. doi:10.1166/jnn.2009.1087.  

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