Niobium(III) chloride

Niobium(III) chloride also known as niobium trichloride is a compound of niobium and chlorine. It is a non-stoichiometric compound, with formula NbClx for 2.667 ≤ x ≤ 3.13.

Niobium(III) chloride
Identifiers
3D model (JSmol)
ChemSpider
Properties
Cl3Nb
Molar mass 199.26 g·mol−1
Appearance black solid
Density 3.75
Structure[1]
hexagonal
P3m1
a = 6.744, c = 12.268
2
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Synthesis

It is produced by reduction of niobium(V) chloride with hydrogen, or just by heating. One end member of the range of composition has formula Nb3Cl8. The dimethoxyethane (dme) adduct of niobium trichloride is produced by reduction of a dme solution of niobium pentachloride with tributyltin hydride:[2]

NbCl5 + 2 Bu3SnH + CH3OCH2CH2OCH3 → NbCl3(CH3OCH2CH2OCH3) + 2 Bu3SnCl

Structure

Nb3Cl8 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. NbCl4 has this pattern of vacancies stretched until the niobium atoms are in pairs rather than triangles. So NbCl3 can be considered as a solid solution of Nb3Cl8 and Nb2Cl8.[3] The triangles of Nb3 and pairs Nb2 in these solid compounds are niobium clusters.

The structure of NbCl3(dimethoxyethane) is unknown. It is unlikely to be monomeric since it forms adducts with alkynes.[4]

Properties

The colour of niobium trichloride varies depending on the chloride ratio from green for NbCl2.67 to brown for NbCl3.13.[1]

Reactions

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

NbCl3(dimethoxyethane) has received significant attention as a reagent for reductive coupling of carbonyls and imines.[5]

Niobium(III) chloride forms many molecular complexes with tertiary phosphines.[6] It is sold as a 1,2-dimethoxyethane complex.

Niobium(III) chloride, in the form of Nb2Cl6 with ligands, is also a metal cluster compound with a double bond between the two niobium atoms. Some known complexes have the following formulae: Nb2Cl6(Me2S)3, Nb2Cl6(PPhMe2)4, Nb2Cl6[o-(AsMe2)2C6H4]2 (diars), Nb2Cl6[MeC(CH2AsMe2)3]2 (triars), Nb2Cl6[Ph2PCH2CH2PPh2]4 (diphos), Nb2Cl6[PhPMe2]4, and yet other ligands such as 1,4-dioxane, diethyl ether, or the crown thioether (SC4H8)3 (which is violet).[7]

References
  1. Gutmann, Viktor (1967). Halogen Chemistry. Elsevier. p. 157. ISBN 978-0-323-14847-4.
  2. Pedersen, Steven F.; Hartung, Jack B.; Roskamp, Eric J.; Dragovich, Peter S. (1992). "Niobium(III) and (IV) Halide Complexes". Inorganic Syntheses. 28. pp. 119–123. doi:10.1002/9780470132609.ch28. ISBN 9780470132609.
  3. Cotton, F. Albert; Wilkinson, Geoffrey (1966). Advanced Inorganic Chemistry: A Comprehensive Text. John Wiley. p. 927.
  4. Arteaga-Müller, Rocío; Tsurugi, Hayato; Saito, Teruhiko; Yanagawa, Masao; Oda, Seiji; Mashima, Kazushi (2009). "New Tantalum Ligand-Free Catalyst System for Highly Selective Trimerization of Ethylene Affording 1-Hexene: New Evidence of a Metallacycle Mechanism". Journal of the American Chemical Society. 131 (15): 5370–5371. doi:10.1021/ja8100837. PMID 20560633.
  5. Roskamp, Carrie A.; Roskamp, Eric J. (2001). "Trichloro(1,2-dimethoxyethane)niobium". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rt202s. ISBN 0471936235.
  6. Sharma, Sangeeta; Vermani, O. P.; Narula, A. K. (January 1996). "Synthesis and structural studies of complexes of niobium(III) chloride with ditertiary phosphines". Indian Journal of Chemistry, Section A. 35A (1). ISSN 0975-0975.
  7. Hagen, A. P. (2009). Inorganic Reactions and Methods, The Formation of Bonds to Transition and Inner-Transition Metals. John Wiley & Sons. pp. 67–69. ISBN 978-0-470-14550-0.
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