Hazard
May evolve fumes of hydrogen chloride.
Keep dry
Chemical Properties
yellow fine crystalline powder
Physical properties
Yellow monoclinic crystals; deliquesces; density 2.75 g/cm3; decomposes in moist air with the evolution of HCl; melts at 204.7°C; vaporizes at 254°C; decomposes in water; soluble in alcohol, hydrochloric acid, chloroform and carbon tetrachloride.
Uses
Lewis acid catalyst in organic synthesis.
Uses
Used to form mixed chloro-aryloxide compounds, such as [Nb(OC6H3-2,6-i-Pr2)2Cl3]2, which form pyridine or phosphine adducts with a distorted six-coordinate geometry.†
Preparation
Niobium pentachloride is obtained as an intermediate during extraction of niobium from its ores (see Niobium). Also, the pentachloride is obtained readily by direct chlorination of niobium metal at 300 to 350°C: 2Nb + 5Cl2 → 2NbCl5
The pentachloride also may be made by chlorination of niobium pentoxide in the presence of carbon at 300°C. The products, however, contain small amounts of niobium oxide trichloride, NbOCl3.
Flammability and Explosibility
Nonflammable
Purification Methods
It forms yellow, very deliquescent crystals which decompose in moist air to liberate HCl. It should be kept in a dry box flushed with N2 in the presence of P2O5. Wash it with CCl4 and dry it over P2O5. The yellow crystals usually contain a few small, dirty white pellets among the yellow needles. These should be easily picked out. Upon grinding in a dry box, however, they turn yellow. NbCl5 has been sublimed and fractionated in an electric furnace. [Epperson Inorg Synth VII 163 1963, Alexander & Fairbrother J Chem Soc suppl 233 1949.] d2 5 20 pK25
