Terbium(III,IV) oxide

Terbium(III,IV) oxide, occasionally called tetraterbium heptaoxide, has the formula Tb4O7, though some texts refer to it as TbO1.75. There is some debate as to whether it is a discrete compound, or simply one phase in an interstitial oxide system. Tb4O7 is one of the main commercial terbium compounds, and the only such product containing at least some Tb(IV) (terbium in the +4 oxidation state), along with the more stable Tb(III). It is produced by heating the metal oxalate, and it is used in the preparation of other terbium compounds. Terbium forms three other major oxides: Tb2O3, TbO2, and Tb6O11.

Terbium(III,IV) oxide
Names
IUPAC name
Tetraterbium heptaoxide
Other names
Terbium(III,IV) oxide,
Terbium peroxide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.031.675
Properties
Tb4O7
Molar mass 747.6972 g/mol
Appearance Dark brown-black
hygroscopic solid.
Density 7.3 g/cm3
Melting point Decomposes to Tb2O3
Insoluble
Hazards
Main hazards Oxidising agent.
Related compounds
Other cations
 Terbium(III) oxide
Terbium(IV) oxide
Related compounds
 Cerium(IV) oxide
Praseodymium(III,IV) oxide
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

Synthesis

Tb4O7 is most often produced by ignition of the oxalate at or the sulfate in air.[1] The oxalate (at 1000 °C) is generally preferred, since the sulfate requires a higher temperature, and it produces an almost black product contaminated with Tb6O11 or other oxygen-rich oxides.

Chemical properties

Terbium(III,IV) oxide loses O2 when heated at high temperatures; at more moderate temperatures (ca. 350 °C) it reversibly loses oxygen, as shown by exchange with18O2. This property, also seen in Pr6O11 and V2O5, allows it to work like V2O5 as a redox catalyst in reactions involving oxygen. It was found as early as 1916 that hot Tb4O7 catalyses the reaction of coal gas (CO + H2) with air, leading to incandescence and often ignition.[2]

Tb4O7 reacts with atomic oxygen to produce TbO2, but a more convenient preparation of TbO2 is by selective dissolving of Tb4O7. This is performed by refluxing with an excess of an equal mixture of concentrated acetic acid and hydrochloric acids for 30 minutes, producing terbium(III) chloride and water.[3]

Tb
4O
7 (s) + 6 HCl (aq) → 2 TbO
2 (s) + 2 TbCl
3 (aq) + 3 H
2O (l)

Tb4O7 reacts with other hot concentrated acids to produce terbium(III) salts. For example, reaction with sulfuric acid gives terbium(III) sulfate. Terbium oxide reacts slowly with hydrochloric acid to form terbium(III) chloride solution, and elemental chlorine. At ambient temperature, complete dissolution might require a month; in a hot water bath, about a week.


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References
  1. Hartmut Bergmann, Leopold Gmelin (1986). Gmelin Handbook of Inorganic Chemistry, System Number 39. Springer-Verlag. p. 397. ISBN 9783540935254.
  2. Bissell, D. W.; James, C. (1916). "GADOLINIUM SODIUM SULFATE". Journal of the American Chemical Society. 38 (4): 873. doi:10.1021/ja02261a012.
  3. Edelmann, F.T.; Poremba, P. (1967). Herrmann, W.A. (ed.). Synthetic Methods of Organometallic and Inorganic Chemistry. 6. Stuttgart: Georg Thieme Verlag. ISBN 3-13-103071-2.

Further reading
  • CRC Handbook of Chemistry and Physics (71st ed.). Ann Arbor, Michigan: CRC Press. 1990. ISBN 978-0-8493-0471-2.
  • Mellor, J.W. A Comprehensive Treatise on Inorganic and Theoretical Chemistry. London: Longmans, Green & Co. pp. 692–696.
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