Niobium(V) ethoxide

Niobium(V) ethoxide is an metalorganic compound with formula Nb2(OC2H5)10. It is a colorless liquid that dissolves in some organic solvents but hydrolyzes readily.[2] It is mainly used for the sol-gel processing of materials containing niobium oxides.[4]

Niobium(V) Ethoxide

Skeletal structure of niobium(V) ethoxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.019.814
EC Number
  • 221-795-2
Properties
C10H25NbO5
Molar mass 318.209 g mol−1
Appearance white solid
Density 1.258 g cm−3
Melting point 5 °C (41 °F; 278 K)
Boiling point 203 °C (397 °F; 476 K)
N/A; reacts with water[2]
Thermochemistry
−1583.9 ± 2.7 kJ mol−1[3]
−6872.6 ± 1.7 kJ mol−1[3]
Hazards
R-phrases (outdated) R10,R34
S-phrases (outdated) S26,S36,S37,S39,S45
NFPA 704 (fire diamond)
Flash point 36 °C; 97 °F; 309 K
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Structure

Metal alkoxides rarely adopt monomeric structures, and niobium(V) ethoxide is no exception. Early studies established that niobium alkoxides aggregate in solution as dimers.[5] Subsequent crystallographic analysis established that the methoxide and isopropoxides of niobium adopt bioctahedral structures.[6] From a geometric perspective, the ten ethoxide ligand oxygen atoms of the Nb2(OEt)10 molecule in solution define a pair of octahedra sharing a common edge with the two niobium atoms located at their centres. From a bonding perspective, each niobium centre is surrounded octahedrally by four monodentate and two bridging ethoxide ligands. The oxygen atoms of the bridging ethoxides are each bonded to both niobium centres, and these two ligands are cis to one another within the coordination sphere. The formula [(EtO)4Nb(μ-OEt)]2 more comprehensively represents this dimeric structure, though the simplified formula is commonly used for most purposes.

Preparation and reactions

This compound is prepared by salt metathesis from niobium pentachloride (Et = C2H5):

10 NaOEt + Nb2Cl10 → Nb2(OC2H5)10 + 10 NaCl

The most important reaction of niobium alkoxides is their hydrolysis to produce films and gels of niobium oxides.[4] Although these reactions are complex, they can be described by this simplified equation:

Nb2(OC2H5)10 + 5 H2O → Nb2O5 + 10 HOEt

The thermal decomposition of Nb(OC2H5)5 begins above 325 – 350 °C. This can be observed with QMS as an increasing amount of ethanol and ethane released. Diethyl ether, C2H5OC2H5, and niobium(V) oxide are the decomposition products released following an atomic layer deposition or chemical vapor deposition process. The decomposition reaction can be summarised as:[7]

Nb2(OC2H5)10 → Nb2O5 + 5 O(C2H5)2

References
  1. "ChemSpider CSID:13600". ChemSpider. Retrieved 17 November 2012.
  2. W. M. Haynes. CRC Handbook of Chemistry and Physics, 93rd Edition. Physical Constants of Inorganic Compounds.
  3. http://webbook.nist.gov/cgi/cbook.cgi?ID=C3236826&Units=SI&Mask=7. Retrieved November 15, 2012.
  4. U. Schubert "Sol–Gel Processing of Metal Compounds" Comprehensive Coordination Chemistry II 2003, Pages 629–656 Volume 7. doi:10.1016/B0-08-043748-6/06213-7
  5. Bradley, D. C.; Holloway, C. E. (1968). "Nuclear Magnetic Resonance Studies on Niobium and Tantalum Penta-alkoxides". J. Chem. Soc. A: 219–223. doi:10.1039/J19680000219.
  6. Mehrotra, Ram C.; Singh, Anirudh (1997). "Recent Trends in Metal Alkoxide Chemistry". In Karlin, Kenneth D. (ed.). Progress in Inorganic Chemistry. 46. John Wiley & Sons. pp. 239–454. doi:10.1002/9780470166475.ch4. ISBN 9780470167045.
  7. Rahtu, Antti (2002). Atomic Layer Deposition of High Permittivity Oxides: Film Growth and In Situ Studies (Thesis). University of Helsinki. hdl:10138/21065. ISBN 952-10-0646-3.
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