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 Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has s ...

. NbCl₅ may be purified by sublimation.

Structure and properties

Niobium-pentachloride-from-xtal-3D-balls

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 length In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...

s 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 In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles ...

at the bridge is 101.3°. The Nb–Nb distance is 398.8 pm, too long for any metal-metal interaction. NbBr₅, TaCl₅ and TaBr₅ are isostructural with NbCl₅, but NbI₅ and TaI₅ have different structures.

Preparation

Industrially, niobium pentachloride is obtained by direct chlorination of niobium metal at 300 to 350 °C: :2Nb + 5Cl₂ → 2NbCl₅ 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 Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...

: It also can be prepared by chlorination of

niobium pentoxide Niobium pentoxide is the inorganic compound with the formula Nb2 O5. A colorless, insoluble, and fairly unreactive solid, it is the most widespread precursor for other compounds and materials containing niobium. It is predominantly used in alloyi ...

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 compound Organoniobium chemistry is the chemistry of compounds containing niobium- carbon (Nb-C) bonds. Compared to the other group 5 transition metal organometallics, the chemistry of organoniobium compounds most closely resembles that of organotantalum co ...

s. In

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

, NbCl₅ is a very specialized

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

in activating

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic ...

s for the

carbonyl-ene reaction In organic chemistry, the ene reaction (also known as the Alder-ene reaction by its discoverer Kurt Alder in 1943) is a chemical reaction between an alkene with an allylic hydrogen (the ene) and a compound containing a multiple bond (the enophile) ...

and the Diels-Alder reaction. Niobium chloride can also generate N-acyliminium compounds from certain

pyrrolidine Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula (CH2)4NH. It is a cyclic secondary amine, also classified as a saturated heterocycle. It is a colourless liquid that is miscible with water and most ...

s which are substrates for

nucleophile In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they ar ...

s such as allyltrimethylsilane,

indole Indole is an aromatic heterocyclic organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other c ...

, or the

silyl enol ether Silyl enol ethers in organic chemistry are a class of organic compounds that share a common functional group composed of an enolate bonded through its oxygen end to an organosilicon group. They are important intermediates in organic synthesis. Sy ...

benzophenone Benzophenone is the organic compound with the formula (C6H5)2CO, generally abbreviated Ph2CO. It is a white solid that is soluble in organic solvents. Benzophenone is a widely used building block in organic chemistry, being the parent diarylket ...

References

External links

Safety information from ChemExper

NIST Standard Reference Database
{{Chlorides Niobium(V) compounds Chlorides Metal halides