Niobium(V) chloride
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| Niobium(V) chloride | |
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_chloride.png/200px-Niobium(V)_chloride.png) |
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| Identifiers | |
| CAS number | [10026-12-7] |
| EINECS number | |
| RTECS number | QU0350000 |
| Properties | |
| Molecular formula | NbCl5 |
| Molar mass | 270.17 g/mol |
| Melting point |
204.7 °C |
| Boiling point |
254 °C |
| Solubility in other solvents | Good |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
-797.47 kJ/mol |
| Standard molar entropy S |
214.05 J.K−1.mol−1 |
| Hazards | |
| EU classification | not listed |
| Flash point | non-flammable |
| Related compounds | |
| Related chlorides | Vanadium(IV) chloride Tantalum(V) chloride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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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.
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[edit] 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.
[edit] 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]
[edit] Bibliography
- Cotton, F. Albert; Wilkinson, Geoffrey (1980). Advanced Inorganic Chemistry (4th Edn.). New York:Wiley. ISBN 0-471-02775-8.
[edit] References
- ^ 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:.
- ^ 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.
