- Niobium(V) chloride
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Niobium(V) chloride 
Niobium(V) chloride
Niobium pentachlorideIdentifiers CAS number 10026-12-7 
EC number 233-059-8 RTECS number QU0350000 Properties Molecular formula NbCl5 Molar mass 270.17 g/mol Appearance yellow monoclinic crystals
deliquescentDensity 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 So298214.05 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) iodideOther cations Vanadium(IV) chloride
Tantalum(V) chlorideRelated niobium chlorides Niobium(III) chloride
Niobium(IV) chloride
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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. 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]
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.[2] NbBr5, TaCl5 and TaBr5 are isostructural with NbCl5, but NbI5 and TaI5 have different structures.
Preparation
Niobium pentachloride liquid and vapor
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, NbCl3 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
- ^ Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, ISBN 0-471-02775-8
- ^ 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 (11): 2435–2437. doi:10.1107/S0108270191000239.
- ^ Joachim Eckert, Hermann C. Starck "Niobium and Niobium Compounds" Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a17_251
- ^ D. Brown "Niobium(V) Chloride and Hexachloroniobates(V)" Inorganic Syntheses, 1957 Volume 9, pp. 88–92.doi:10.1002/9780470132401.ch24
- ^ 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 (3b): 535–539. doi:10.1590/S0103-50532005000400007. http://jbcs.sbq.org.br/online/2005/vol16_n3B/06-144-04.pdf.
External links
Niobium compounds Categories:- Niobium compounds
- Chlorides
- Metal halides
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