Niobium oxychloride explained

Niobium oxychloride is the inorganic compound with the formula NbOCl₃. It is a white, crystalline, diamagnetic solid. It is often found as an impurity in samples of niobium pentachloride, a common reagent in niobium chemistry.

Structure

In the solid state the coordination sphere for niobium is a distorted octahedron. The Nb–O bonds and Nb–Cl bonds are unequal. This structure can be described as planar Nb₂Cl₆ core connected by O–Nb–O bridges. In this way, the compound is best described as a polymer, consisting of a double stranded chain.^{[1] [2]}

In the gas phase above 320 °C the Raman spectrum is consistent with a pyramidal monomer containing a niobium–oxygen double bond.^[3]

Synthesis

Niobium oxychloride is prepared by treating the pentachloride with oxygen:^[4]

NbCl₅ +  O₂ → NbOCl₃ + Cl₂

This reaction is conducted at about 200 °C. NbOCl₃ also forms as a major side-product in the reaction of niobium pentoxide with various chlorinating agents such as carbon tetrachloride and thionyl chloride.^{[4] [5]}

2 Nb₂O₅ + 6 CCl₄ → 4 NbOCl₃ + 6 COCl₂

References

1. Ströbele . Markus . Meyer . Hans-Jürgen . 2002 . Neubestimmung der Kristallstruktur von NbOCl₃ . Zeitschrift für anorganische und allgemeine Chemie . 628 . 2. 488–491 . 10.1002/1521-3749(200202)628:2<488::AID-ZAAC488>3.0.CO;2-B .
2. 10.1002/zaac.200500041 . Polar [NbOCl₃]_2n and [{{chem|NbOX|4|−}}]_n (X = Cl, Br) Chains in the Structures of NbOCl₃ and the Thallium-Halogenooxoniobates Tl[NbOCl₄] and Tl[NbOBr₄] — Synthesis, Crystal Structures and Optical Second Harmonic Generation . 2005 . Beck . Johannes . Bordinhão . Jairo . Zeitschrift für anorganische und allgemeine Chemie . 631 . 6–7 . 1261–1266.
3. Book: Greenwood, N. N. . Spectroscopic Properties of Inorganic and Organometallic Compounds . Royal Society of Chemistry . January 1, 1970 . 196 . Chapter 5: Vibrational Spectra . 9780851860237.
4. Book: Niobium Oxytrichloride. Handbook of Preparative Inorganic Chemistry. 2nd. Brauer. G.. G. Brauer. Academic Press. 1963. New York. 2. 1307.
5. 10.1007/s11663-997-0125-0 . Kinetics of chlorination of niobium pentoxide by carbon tetrachloride . 1997 . Jena . P. K. . Brocchi . E. A. . Garcia . R. I. . Metallurgical and Materials Transactions B . 28 . 1 . 39–45. 1997MMTB...28...39J . 98226151 . .