Niobium(V) chloride: Difference between revisions

| verifiedrevid = 390833027

| Name = Niobium(V) chloride

| ImageFile = Niobium pentachloride solid.jpg

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| ImageName = Sample of niobium(V) chloride

| ImageFile1 = Niobium-pentachloride-dimer-2D.png

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| ImageName2 = Niobium pentachloride liquid and vapor

| IUPACName = Niobium(V) chloride<br/>Niobium pentachloride

| Section1 = {{Chembox Identifiers

| CASNo = 10026-12-7

| CASNo_Ref = {{cascite|correct|CAS}}

| EINECS = 233-059-8

| RTECS = QU0350000

| Section2 = {{Chembox Properties

| Formula = NbCl₅

| Appearance = yellow [[monoclinic]] crystals <br> [[deliquescent]]

| MolarMass = 270.17 g/mol

| Density = 2.75 g/cm³

| Solubility = decomposes

| SolubleOther = soluble in [[alcohol]], [[hydrochloric acid|HCl]], [[chloroform]], [[carbon tetrachloride|CCl₄]]

| MeltingPt = 204.7 °C

| BoilingPt = 248.2 °C

| Section4 = {{Chembox Thermochemistry

| DeltaHf = -797.47 kJ/mol

| Entropy = 214.05 J&thinsp;K⁻¹&thinsp;mol⁻¹

| Section7 = {{Chembox Hazards

| ExternalMSDS =

| EUIndex = Not listed

| FlashPt = Non-flammable

| PEL =

| Section8 = {{Chembox Related

| OtherAnions = [[Niobium(V) fluoride]]<br/>[[Niobium(V) bromide]]<br/>[[Niobium(V) iodide]]

| OtherCations = [[Vanadium(IV) chloride]]<br/>[[Tantalum(V) chloride]]

| OtherFunctn = [[Niobium(III) chloride]]<br/>[[Niobium(IV) chloride]]

| Function = niobium chlorides

'''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 (physics)|sublimation]].<ref>{{Cotton&Wilkinson4th}}</ref>

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&ndash;chlorine [[bond length]]s are 225&nbsp;pm (terminal) and 256&nbsp;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&ndash;Cl&ndash;Nb [[bond angle|angle]] at the bridge is 101.3°. The Nb&ndash;Nb distance is 398.8&nbsp;pm, too long for any metal-metal interaction.<ref name = cotton>{{cite journal | author = Cotton, F.A., P. A. Kibala, M. Matusz and R. B. W. Sandor | year = 1991 | title = Structure of the Second Polymorph of Niobium Pentachloride | journal = [[Acta Cryst.]] | volume = C47 | pages = 2435–2437 | doi = 10.1107/S0108270191000239}}</ref> NbBr₅, [[Tantalum(V) chloride|TaCl₅]] and TaBr₅ are isostructural with NbCl₅, but NbI₅ and TaI₅ have different structures.

[[File:Niobium pentachloride2.jpg|150px|thumb|left|Niobium pentachloride liquid and vapor]]

Industrially, niobium pentachloride is obtained by direct chlorination of niobium metal at 300 to 350 °C:<ref name=Ullmann>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}}</ref>

: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]]:<ref>D. Brown "Niobium(V) Chloride and Hexachloroniobates(V)" Inorganic Syntheses, 1957 Volume 9, pp. 88–92.{{DOI|10.1002/9780470132401.ch24}}</ref> 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 [[Niobium oxychloride|NbOCl₃]].

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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 [[alkene]]s for the [[carbonyl-ene reaction]] and the [[Diels-Alder]] reaction. Niobium chloride can also generate N-acyliminium compounds from certain [[pyrrolidine]]s which are substrates for [[nucleophile]]s such as allyltrimethylsilane, [[indole]], or the [[silyl enol ether]] of [[benzophenone]].<ref>{{cite journal | author = Andrade, C. K. Z.; Rocha, R. O.; Russowsky, D.; & Godoy, M. N. | year = 2005 | title = Studies on the Niobium Pentachloride-Mediated Nucleophilic Additions to an Enantiopure Cyclic N-acyliminium Ion Derived from (''S'')-malic acid | journal = J. Braz. Chem. Soc. | volume = 16 | pages = 535–539 | url = http://jbcs.sbq.org.br/online/2005/vol16_n3B/06-144-04.pdf | doi = 10.1590/S0103-50532005000400007}}</ref>

[[Category:Niobium compounds]]

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