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In chemistry, hypomanganate, also called manganate(V) or tetraoxidomanganate(3−), is a trivalent anion (electric charge ion) composed of manganese and oxygen, with formula .
Hypomanganates are usually bright blue.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. Potassium hypomanganate is the best known salt, but sodium hypomanganate , barium hypomanganate , and the mixed potassium-barium salt is also known. The anion can replace phosphate in synthetic variants of the minerals apatiteK. 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. 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 and brownmillerite.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 " Inorganic Chemistry, volume 52, issue 3, pages 1349-1357.
The anion is a bright blue species. with a visible absorption maximum at wavelength λmax = 670 nm ( ε = )..
The disproportionation is believed to pass through a protonated intermediate, with the acid dissociation constant for the reaction HMnO MnO + H+ being estimated as p Ka = .. However, K3MnO4 has been cocrystallized with Ca2Cl(PO4), allowing the study of the UV–visible spectrum of the hypomanganate ion..
Hypomanganates can also be prepared by the solid state method under flow near 1000 °C. They can be prepared also via low temperature routes such as hydrothermal synthesis or flux growth. It is produced by dissolving manganese dioxide in molten sodium nitrite.
The barium salt has interesting magnetic properties.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 ". Physics Review B, volume 77, page 134406
Cyclic of hypomanganic acid are thought to be intermediates in the oxidation of by permanganate.
History
The manganate(V) anion was first reported in 1946 by Hermann Lux, who synthesized the intensely blue sodium hypomanganate by reacting sodium oxide and manganese dioxide in fused sodium nitrite at 500 °C.Herrman Lux (1946): " Über Salze des fünfwertigen Mangans." Zeitschrift für Naturforschung, volume 1, pages 281-283. He also crystalized the salt from strong (50%) sodium hydroxide solutions as the hydrate ·10.
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 state ground state.
Stability
Hypomanganate is unstable towards disproportionation to manganate and manganese dioxide:. The estimated electrode potentials at pH 14 are:...
However, the reaction is slow in very alkaline solutions (with OH− concentration above 5–10 mol/liter).
Preparation
Hypomanganates may be prepared by the careful reduction of manganates with sulfite, hydrogen peroxide. or Mandelic acid.
Uses
The strontium vanadate fluoride compound, with hypomanganate substituted for some vanadate units, has been investigated for potential use in near infrared lasers.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.
Related compounds
In theory, hypomanganate would be the conjugate base of hypomanganic acid . This acid cannot be formed because of its rapid disproportionation, but its third acid dissociation constant has been estimated by pulse radiolysis techniques:
See also
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