Niobium(V) chloride

Niobium(V) chloride, also known as niobium pentachloride, is a chemical compound with the formula NbCl₅. This yellow solid is an important reagent in the synthesis of niobium compounds, serving as a starting material for a variety of niobium-based materials and catalysts. It is highly reactive and acts as a Lewis acid in various chemical reactions.

Properties

Niobium(V) chloride is a yellow, volatile solid at room temperature. It has a high melting point and sublimes readily at slightly above room temperature. It is soluble in polar solvents such as alcohols, ethers, and chlorinated solvents, forming adducts. In its solid form, NbCl₅ adopts a dimeric structure, with two NbCl₅ units sharing a chlorine atom.

Synthesis

Niobium(V) chloride can be synthesized by the direct chlorination of niobium metal under the appropriate conditions. The reaction typically involves the use of chlorine gas at elevated temperatures:

\[ \text{2 Nb} + \text{5 Cl}_2 \rightarrow \text{2 NbCl}_5 \]

Alternatively, it can be produced by the reaction of niobium pentoxide (Nb₂O₅) with thionyl chloride (SOCl₂), followed by purification.

Reactivity and Uses

Niobium(V) chloride is a versatile reagent in the synthesis of organoniobium compounds. It acts as a Lewis acid, forming complexes with various ligands. This property is exploited in its use as a catalyst in organic synthesis, including polymerization reactions and the alkylation of aromatics.

In addition to its role as a catalyst, NbCl₅ is a precursor to other niobium compounds, including oxides and halides. It is also used in the preparation of niobium metal through reduction processes.

Safety

Niobium(V) chloride is corrosive and reacts violently with water, releasing hydrochloric acid (HCl). It should be handled with care, using appropriate personal protective equipment and in a well-ventilated area or fume hood. Storage should be in a cool, dry place, away from moisture and incompatible materials.

See Also

• Niobium
• Lewis acids and bases
• Organometallic chemistry
• Catalysis