my-server
← Wiki Redirected from Niobium trichloride

Niobium(III) chloride

Niobium(III) chloride also known as niobium trichloride is a compound of niobium and chlorine. The binary phase NbCl<sub>3</sub> is not well characterized but many adducts are known.

Structure

Nb<sub>3</sub>Cl<sub>8</sub> has a hexagonal close packed 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 compounds. NbCl<sub>4</sub> has this pattern of vacancies stretched until the niobium atoms are in pairs rather than triangles. So NbCl<sub>3</sub> can be considered as a solid solution of Nb<sub>3</sub>Cl<sub>8</sub> and Nb<sub>2</sub>Cl<sub>8</sub>.

The colour of niobium trichloride varies depending on the niobium:chloride ratio. NbCl<sub>2.67</sub> is green, while NbCl<sub>3.13</sub> is brown.

Synthesis

Nb<sub>3</sub>Cl<sub>8</sub> is produced by reduction of niobium(V) chloride with hydrogen, or just by heating.

Salt-free reduction of dimethoxyethane solution of NbCl<sub>5</sub> with 1,4-disilyl-cyclohexadiene in the presence of 3-hexyne produces the coordination complex NbCl<sub>3</sub>(dimethoxyethane)(3-hexyne):

NbCl<sub>5</sub> + C<sub>6</sub>H<sub>6</sub>(SiMe<sub>3</sub>)<sub>2</sub> + C<sub>2</sub>Et<sub>2</sub> + dme → NbCl<sub>3</sub>(dme)(C<sub>2</sub>Et<sub>2</sub>) + C<sub>6</sub>H<sub>6</sub> + 2 Me<sub>3</sub>SiCl

An impure dimethoxyethane (dme) adduct of niobium trichloride was produced by reduction of a dme solution of niobium pentachloride with tributyltin hydride:

NbCl<sub>5</sub> + 2&nbsp;Bu<sub>3</sub>SnH + MeOCH<sub>2</sub>CH<sub>2</sub>OMe → NbCl<sub>3</sub>(MeOCH<sub>2</sub>CH<sub>2</sub>OMe) + 2&nbsp;Bu<sub>3</sub>SnCl

Reactions

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

Adducts

NbCl<sub>3</sub>(dimethoxyethane) has received significant attention as a reagent for reductive coupling of carbonyls and imines. It is sold as a 1,2-dimethoxyethane complex. Nb(III) adducts are also known for 1,4-dioxane and diethyl ether.

Niobium(III) chloride forms a series of compounds with the formula Nb<sub>2</sub>Cl<sub>6</sub>L<sub>x</sub> with Nb=Nb double bond. With tertiary phosphines and arsines, the complexes are edge-share bioctahedra, e.g., Nb<sub>2</sub>Cl<sub>6</sub>(PPhMe<sub>2</sub>)<sub>4</sub>. Thioethers form adducts with one bridging thioether (R<sub>2</sub>S). These face-sharing bioctahedra have the formula Nb<sub>2</sub>X<sub>6</sub>(R<sub>2</sub>S)<sub>3</sub> (X = Cl, Br).

References