Niobium(III) chloride also known as niobium trichloride is a compound 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 sim ...

and

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

. The binary phase NbCl₃ is not well characterized but many adducts are known.

Synthesis

left, 184px, Structure of NbCl₃(dimethoxyethane)(3-hexyne). Nb₃Cl₈ is produced by reduction of

niobium(V) chloride 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. NbCl ...

with

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

, or just by heating.

Salt-free reduction In chemistry, salt-free reduction describes methodology for reduction of metal halides by electron-rich trimethylsilyl reagents. Traditional reductions of metal halides are accomplished with alkali metals, a process that cogenerates alkali metal s ...

of dimethoxyethane solution of NbCl₅ with 1,4-disilyl-cyclohexadiene in the presence of 3-hexyne produces the

coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

NbCl₃(dimethoxyethane)(3-hexyne): : NbCl₅ + C₆H₆(SiMe₃)₂ + C₂Et₂ + dme → NbCl₃(dme)(C₂Et₂) + C₆H₆ + 2 Me₃SiCl An impure

dimethoxyethane Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve, and DME, is a colorless, aprotic, and liquid ether that is used as a solvent, especially in batteries. Dimethoxyethane is misci ...

(dme) adduct of niobium trichloride was produced by reduction of a dme solution of niobium pentachloride with

tributyltin hydride Tributyltin hydride is an organotin compound with the formula (C4H9)3SnH. It is a colorless liquid that is soluble in organic solvents. The compound is used as a source of hydrogen atoms in organic synthesis. Synthesis and characterization The ...

: :NbCl₅ + 2 Bu₃SnH + MeOCH₂CH₂OMe → NbCl₃(MeOCH₂CH₂OMe) + 2 Bu₃SnCl

Structure

Nb₃Cl₈ has a

hexagonal close packed In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...

array of chloride ions. Triangles of niobium occur in octahedral spaces in the chloride array. The compositions with higher chloride have some niobium atoms missing from the structure, creating vacancies and giving rise to

nonstoichiometric compound In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); mos ...

s. NbCl₄ has this pattern of vacancies stretched until the niobium atoms are in pairs rather than triangles. So NbCl₃ can be considered as a solid solution of Nb₃Cl₈ and Nb₂Cl₈. The colour of niobium trichloride varies depending on the niobium:chloride ratio. NbCl_2.67 is green, while NbCl_3.13 is brown.

Reactions

When heated to over 600 °C niobium trichloride disproportionates to niobium metal and niobium pentachloride.

Adducts

NbCl₃(dimethoxyethane) has received significant attention as a reagent for reductive coupling of carbonyls and imines. It is sold as a

1,2-dimethoxyethane Dimethoxyethane, also known as glyme, monoglyme, dimethyl glycol, ethylene glycol dimethyl ether, dimethyl cellosolve, and DME, is a colorless, aprotic, and liquid ether that is used as a solvent, especially in batteries. Dimethoxyethane is misc ...

complex. Nb(III) adducts are also known for

1,4-dioxane 1,4-Dioxane () is a heterocyclic organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other dioxane isomers ( 1,2- ...

and

diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...

. Niobium(III) chloride forms a series of compounds with the formula Nb₂Cl₆L_x with Nb=Nb double bond. With tertiary phosphines and arsines, the complexes are edge-share bioctahedra, e.g., Nb₂Cl₆(PPhMe₂)₄. Thioethers form adducts with one bridging thioether (R₂S). These face-sharing bioctahedra have the formula Nb₂X₆(R₂S)₃ (X = Cl, Br).

References

{{Chlorides Niobium(III) compounds Chlorides Non-stoichiometric compounds