Niobium(V) chloride

Niobium(V) chloride
Names
	IUPAC names Niobium(V) chloride; Niobium pentachloride
Identifiers
CAS Number	10026-12-7 NbCl5 [chemspider];
3D model (JSmol)	Interactive image; dimer: Interactive image;
ChemSpider	23203;
ECHA InfoCard	100.030.042
EC Number	233-059-8;
PubChem CID	24818;
RTECS number	QU0350000;
UNII	9S1BC7865F ;
CompTox Dashboard (EPA)	DTXSID7044348 ;
	InChI InChI=1S/5ClH.Nb/h5*1H;/q;;;;;+5/p-5 Key: YHBDIEWMOMLKOO-UHFFFAOYSA-I;
	SMILES Cl[Nb](Cl)(Cl)(Cl)Cl; dimer: Cl[Nb-]1(Cl)(Cl)(Cl)[Cl+][Nb-]([Cl+]1)(Cl)(Cl)(Cl)Cl;
Properties
Chemical formula	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)
Solubility in water	decomposes
Solubility	HCl, chloroform, CCl4
Thermochemistry
Std molar; entropy (So298)	214.05 J K−1 mol−1
Std enthalpy of; formation (ΔfH⦵298)	-797.47 kJ/mol
Hazards
GHS pictograms
GHS Signal word	Danger
GHS hazard statements	H302, H312, H314, H332
GHS precautionary statements	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

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]

Structure and properties

Ball-and-stick model of niobium pentachloride

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 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.

Uses

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]

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 Crystallogr. C. 47 (11): 2435–2437. doi:10.1107/S0108270191000239.CS1 maint: multiple names: authors list (link)
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. ISBN 3527306730.CS1 maint: uses authors parameter (link)
Brown, D. (1957). "Niobium(V) Chloride and Hexachloroniobates(V)". Inorganic Syntheses. 9: 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" (PDF). J. Braz. Chem. Soc. 16 (3b): 535–539. doi:10.1590/S0103-50532005000400007. Archived from the original (PDF) on 2007-10-12.

External links

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[1] Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, ISBN 0-471-02775-8

[cotton-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)

[Ullmann-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. ISBN 3527306730.CS1 maint: uses authors parameter (link)

[4] Brown, D. (1957). "Niobium(V) Chloride and Hexachloroniobates(V)". Inorganic Syntheses. 9: 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.