Niobium(IV) chloride

Niobium(IV) chloride

Names
IUPAC name Niobium(IV) chloride
Other names Niobium tetrachloride Niobium chloride
Identifiers
CAS Number	13569-70-5
PubChem	83583
Properties
Chemical formula	NbCl4
Molar mass	234.718 g/mol
Appearance	Violet-Black Crystals
Density	3.2 g/cm^3
Melting point	Dec. 800 °C
Boiling point	Subl. 275 °C/10^−4 mmHg
Solubility in water	Reacts
Related compounds
Other anions	Niobium(IV) bromide Niobium(IV) iodide
Other cations	Vanadium(IV) chloride Tantalum(IV) chloride
Related niobium chlorides [1]	Niobium(III) chloride Niobium(V) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Niobium(IV) chloride, also known as niobium tetrachloride, is the chemical compound of formula NbCl₄. This compound exists as dark violet crystals, is highly sensitive to air and moisture, and disproportiates into niobium(III) chloride and niobium(V) chloride when heated.^[2]

Structure and properties

In the solid state, niobium(IV) chloride exists as chains of edge-sharing octahedra with alternating Nb-Nb distances of lengths 302.9 and 379.4 pm. The shorter distances correspond to Nb-Nb bonds, forming a polymer resulting in the compound’s diamagnetism. This metal bond forms as niobium forms d¹ compounds in its +4 oxidation state, resulting in lone electrons. Other coordination complexes with the formula NbCl₄L₂, such as tetrachlorobis(tetrahydrofuran) niobium, only form monomers resulting in one unpaired electron in the d_xy orbital, making the compounds paramagnetic.^[3]

Niobium chloride rapidly oxidizes and hydrolyzes in air to form niobium(V) oxide.

Preparation

Niobium(IV) chloride is typically produced by allowing elemental niobium and niobium(V) chloride crystals to react over several days in a temperature gradient, with the metal around 400 °C and the salt around 250 °C.^[4]

4 NbCl₅ + Nb → 5 NbCl₄

Niobium (IV) chloride can also prepared by a similar reduction of niobium pentachloride with powdered aluminium.

3 NbCl₅ + Al → 3 NbCl₄ + AlCl₃

A similar technique is also used in the synthesis of niobium(IV) bromide and tantalum(IV) chloride. Niobium(IV) iodide exists as well and may be synthesized by thermal decomposition of niobium(V) iodide.

At 400 °C NbCl₄ disproportiates:

2 NbCl₄ → NbCl₃ + NbCl₅

Reactions

The disproportiation of niobium(IV) chloride can be used to make tetrachlorobis(tetrahydrofuran) niobium, a useful synthon in Nb^IV chemistry due to the lability of the attached tetrahydrofuran ligands.^[5] This compound can be synthesized by first reacting NbCl₅ with aluminium in acetonitrile followed by addition of tetrahydrofuran to the resultant solid by the following reaction.^[6]

3 NbCl₅ + Al + 3 CH₃CN → 3 NbCl₄(NCCH₃)₃ + AlCl₃

3 NbCl₄(NCCH₃)₃ + AlCl₃ + 3 C₄H₈O → 3 NbCl₄(thf)₂ + 9 MeCN + AlCl₃(thf)

Niobium chloride has been used in the syntheses of indazoles which can be used as LXR or Liver X receptor inhibitors.

References

1. CRC, Handbook of Chemistry and Physics, 89th Ed., 2008/09, editor D. Lide, Cleveland, OH: CRC Press, p. 4-36.
2. Macintyre, J.E.; Daniel, F.M.; Chapman and Hall; Stirling, V.M. Dictionary of Inorganic Compounds. 1992, Cleveland, OH: CRC Press, p. 2957
3. Cotton, F. A..; Lu, J. (1995). "EPR and Crystallographic Studies of Some Reaction Products of VCl₄, NbCl₄, and TaCl₄ with Trialkyl- and Triarylphosphines". Inorg. Chem. 34 (10): 2639. doi:10.1021/ic00114a023.
4. McCarley, Robert E.; Torp, Bruce A. (1963). "The preparation and properties of niobium(IV) compounds. I. Some niobium(IV) halides and their pyridine adducts". Inorg. Chem. 2 (3): 540. doi:10.1021/ic50007a029.
5. Hubert-Pfalzgraf, L.G. Niobium & Tantalum: Inorganic & Coordination Chemistry. 2006: John Wiley & Sons, Ltd.
6. Manzer, L.E. (1977). "Preparation of the paramagnetic alkyls bis(cyclopentadienyl)dimethylniobium and bis(methylcyclopentadienyl)dimethyltantalum and some six- and eight-coordinate phosphine derivatives of niobium(IV)". Inorg. Chem. 16 (3): 525. doi:10.1021/ic50169a004.