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Names | |
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IUPAC names Niobium(V) chloride Niobium pentachloride | |
Identifiers | |
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3D model (JSmol) | |
ChemSpider | |
ECHA InfoCard | 100.030.042 |
EC Number |
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PubChem CID | |
RTECS number |
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UNII | |
CompTox Dashboard (EPA) | |
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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 | |
Std molar entropy (S⦵298) | 214.05 J K−1 mol−1 |
Std enthalpy of formation (ΔfH⦵298) | −797.47 kJ/mol |
Hazards | |
GHS labelling: | |
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Danger | |
H302, H312, H314, H332 | |
P260, P261, P264, P270, P271, P280, P301+P312, P301+P330+P331, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, 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). |
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 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, NbI5, TaCl5 TaBr5 and TaI5 are isostructural with NbCl5.
Industrially, niobium pentachloride is obtained by direct chlorination of niobium metal at 300 to 350 °C: [3]
In the laboratory, niobium pentachloride is often prepared from Nb2O5, the main challenge being incomplete reaction to give NbOCl3. 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.
Niobium(V) chloride is the main precursor to the alkoxides of niobium, which find uses in sol-gel processing. It is also the precursor to many other Nb-containing reagents, including most organoniobium compounds.
In organic synthesis, NbCl5 is a very 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]
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