Chemistry:Hypomanganate

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Short description: Trivalent anion

In chemistry, hypomanganate, also called manganate(V) or tetraoxidomanganate(3−), is a trivalent anion (negative ion) composed of manganese and oxygen, with formula MnO3−4.

Hypomanganates are usually bright blue.[1][2] Potassium hypomanganate K3MnO4 is the best known salt, but sodium hypomanganate Na3MnO4, barium hypomanganate Ba3(MnO4)2, and the mixed potassium-barium salt KBaMnO4 is also known.[3] The anion can replace phosphate PO3−4 in synthetic variants of the minerals apatite[4][5] and brownmillerite.[6]

History

The manganate(V) anion was first reported in 1946 by Hermann Lux, who synthesized the intensely blue sodium hypomanganate by reacting sodium oxide Na2O and manganese dioxide MnO2 in fused sodium nitrite NaNO2 at 500 °C.[7][3] He also crystalized the salt from strong (50%) sodium hydroxide solutions as the decahydrate Na3MnO4·10H2O.

Structure and properties

Manganate(V) is a tetrahedral oxyanion structurally similar to sulfate, manganate, and permanganate. As expected for a tetrahedral complex with a d2 configuration, the anion has a triplet ground state.[3]

The anion is a bright blue species[1] with a visible absorption maximum at wavelength λmax = 670 nm (ε = 900 dm3 mol−1 cm−1).[8][9]

Stability

Hypomanganate is unstable towards disproportionation to manganate(VI) and manganese dioxide:[10][1] The estimated electrode potentials at pH 14 are:[11][12][13]

MnO2−4 + e− ⇌ MnO3−4   E = +0.27 V
MnO3−4 + e− + 2 H2O ⇌ MnO2 + 4 OH−   E = +0.96 V

However, the reaction is slow in very alkaline solutions (with OH− concentration above 5–10 mol/L.[1][7]

The disproportionation is believed to pass through a protonated intermediate,[13] with the acid dissociation constant for the reaction HMnO2−4 ⇌ MnO3−4 + H+ being estimated as pKa = 13.7 ± 0.2.[14] However, K3MnO4 has been cocrystallized with Ca2Cl(PO4), allowing the study of the UV–visible spectrum of the hypomanganate ion.[10][15]

Preparation

Hypomanganates may be prepared by the careful reduction of manganates with sulfite,[1] hydrogen peroxide[16] or mandelate.[9]

Hypomanganates can also be prepared by the solid state method under O2 flow near 1000 °C.[3][4][5] [6] They can be prepared also via low temperature routes such as hydrothermal synthesis or flux growth.[3] It is produced by dissolving manganese dioxide in molten sodium nitrite.[17]

Uses

The strontium vanadate fluoride Sr5(VO4)3F compound, with hypomanganate substituted for some vanadate units, has been investigated for potential use in near infrared lasers.[18]

The barium salt Ba3(MnO4)2 has interesting magnetic properties.[19]

Related compounds

In theory, hypomanganate would be the conjugate base of hypomanganic acid H3MnO4. This acid cannot be formed because of its rapid disproportionation, but its third acid dissociation constant has been estimated by pulse radiolysis techniques:[14]

HMnO2−4 ⇌ MnO3−4 + H+   pKa = 13.7 ± 0.2

Cyclic esters of hypomanganic acid are thought to be intermediates in the oxidation of alkenes by permanganate.[9]

See also

  • Dimanganite, a manganate(III) anion Mn2O6−6
  • Manganate or manganate(VI), MnO2−4
  • Permanganate or manganate(VII), MnO−4

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1221–22. ISBN 978-0-08-022057-4. https://books.google.com/books?id=OezvAAAAMAAJ&q=0-08-022057-6&dq=0-08-022057-6&source=bl&ots=m4tIRxdwSk&sig=XQTTjw5EN9n5z62JB3d0vaUEn0Y&hl=en&sa=X&ei=UoAWUN7-EM6ziQfyxIDoCQ&ved=0CD8Q6AEwBA. .
  2. ↑ D. Reinen, W. Rauw, U. Kesper, M. Atanasov, H. U Güdel, M. Hazenkamp, and U. Oetliker (1997): "Colour, luminescence and bonding properties of tetrahedrally coordinated chromium(IV), manganese(V) and iron(VI) in various oxide ceramics" Journal of Alloys and Compounds, volume 246, issue 1-2, pages 193-208. doi:10.1016/S0925-8388(96)02461-9
  3. ↑ 3.0 3.1 3.2 3.3 3.4 zur Loye, K. D.; Chance, W. M.; Yeon, J.; zur Loye, H.-C. (2014). "Synthesis, Crystal Structure, and Magnetic Properties of the Oxometallates KBaMnO4 and KBaAsO4". Solid State Sciences 37: 86–90. doi:10.1016/j.solidstatesciences.2014.08.013. Bibcode: 2014SSSci..37...86Z. 
  4. ↑ 4.0 4.1 K. Dardenne, D. Vivien, and D. Huguenin (1999): "Color of Mn(V)-substituted apatites A10((B, Mn)O4)6F2, A = Ba, Sr, Ca; B= P, V". Journal of Solid State Chem.istry, volume 146, issue 2, pages 464-472. doi:10.1006/jssc.1999.8394
  5. ↑ 5.0 5.1 Grisafe, D.A. and Hummel, F.A. (1970): "Pentavalent ion substitutions in the apatite structure, part A: Crystal chemistry". Journal of Solid State Chemistry, volume 2, issue 2, pages 160-166 doi:10.1016/0022-4596(70)90064-2
  6. ↑ 6.0 6.1 P. Jiang, J. Li, A. Ozarowski, A. W. Sleight, and M. A, Subramanian (2013): "Intense turquoise and green colors in brownmillerite-type oxides based on Mn5+ in Ba2In2-xMnxO5+x" Inorganic Chemistry, volume 52, issue 3, pages 1349-1357. doi:10.1021/ic3020332
  7. ↑ 7.0 7.1 Herrman Lux (1946): "Über Salze des fünfwertigen Mangans." Zeitschrift für Naturforschung, volume 1, pages 281-283.
  8. ↑ Carrington, A.; Symons, M. C. R. (1956), "Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions", J. Chem. Soc.: 3373–80, doi:10.1039/JR9560003373 
  9. ↑ 9.0 9.1 9.2 Lee, Donald G.; Chen, Tao (1993), "Reduction of manganate(VI) by mandelic acid and its significance for development of a general mechanism of oxidation of organic compounds by high-valent transition metal oxides", J. Am. Chem. Soc. 115 (24): 11231–36, doi:10.1021/ja00077a023 .
  10. ↑ 10.0 10.1 Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, p. 746, ISBN 0-471-02775-8 .
  11. ↑ Weast, Robert C., ed (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. D-134. ISBN 0-8493-0462-8. .
  12. ↑ Manganese – compounds – standard reduction potentials, WebElements, http://www.webelements.com/manganese/compounds.html, retrieved 2010-06-26 .
  13. ↑ 13.0 13.1 Sekula-Brzezińska, K.; Wrona, P. K.; Galus, Z. (1979), "Rate of the MnO4−/MnO42− and MnO42−/MnO43− electrode reactions in alkaline solutions at solid electrodes", Electrochim. Acta 24 (5): 555–63, doi:10.1016/0013-4686(79)85032-X .
  14. ↑ 14.0 14.1 Rush, J. D.; Bielski, B. H. J. (1995), "Studies of Manganate(V), -(VI), and -(VII) Tetraoxyanions by Pulse Radiolysis. Optical Spectra of Protonated Forms", Inorg. Chem. 34 (23): 5832–38, doi:10.1021/ic00127a022 .
  15. ↑ Carrington, A.; Symons, M. C. R. (1956), "Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions", J. Chem. Soc.: 3373–80, doi:10.1039/JR9560003373 .
  16. ↑ Lee, Donald G.; Chen, Tao (1989), "Oxidation of hydrocarbons. 18. Mechanism of the reaction between permanganate and carbon-carbon double bonds", J. Am. Chem. Soc. 111 (19): 7534–38, doi:10.1021/ja00201a039 .
  17. ↑ Temple, R. B.; Thickett, G. W. (1972). "The formation of manganese(v) in molten sodium nitrite". Australian Journal of Chemistry 25 (3): 55. doi:10.1071/CH9720655. 
  18. ↑ L. D. Merkle, Y. Guyot, and B. H. T. Chai (1995): "Spectroscopic and laser investigations of Mn5+:Sr5(VO4)3F". Journal of Applied Physics, volume 77, issue 2, pages 474-480. doi:10.1063/1.359585
  19. ↑ M. B. Stone, M. D. Lumsden, Y. Qiu, E. C. Samulon, C. D. Batista, and I. R. Fisher (2008): "Dispersive magnetic excitations in the S=1 antiferromagnet Ba3Mn2O8". Physics Review B, volume 77, page 134406 doi:10.1103/PhysRevB.77.134406



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