View source for Hypomanganate

{{short description|Trivalent anion}}

In [[chemistry]], '''hypomanganate''', also called '''manganate(V)''' or '''tetraoxidomanganate(3−)''', is a [[trivalent]] [[anion]] ([[electric charge|negative]] [[ion]]) composed of [[manganese]] and [[oxygen]], with formula {{chem|MnO|4|3-}}.  

Hypomanganates are usually bright blue.<ref name="G&E"/><ref name=Reinen>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}}</ref> [[Potassium hypomanganate]] {{chem|K|3|MnO|4}} is the best known [[salt (chemistry)|salt]], but [[sodium hypomanganate]] {{chem|Na|3|MnO|4|}}, [[barium hypomanganate]] {{chem|Ba|3|(|MnO|4|)|2}}, and the mixed potassium-barium salt {{chem|KBaMnO|4}} is also known.<ref name=Loye/>   The anion can replace [[phosphate]] {{chem|PO|4|3-}} in synthetic variants of the minerals [[apatite]]<ref name=Dardenne>K. Dardenne, D. Vivien, and D. Huguenin (1999): "Color of Mn(V)-substituted apatites A<sub>10</sub>((B, Mn)O<sub>4</sub>)<sub>6</sub>F<sub>2</sub>, 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}}</ref><ref name=Grisafe> 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}}</ref> and [[brownmillerite]].<ref name=Jiang>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 Mn<sup>5+</sup> in {{chem|Ba|2|In|2-''x''|Mn|''x''|O|5+''x''}}" ''Inorganic Chemistry'', volume 52, issue 3, pages 1349-1357. {{doi|10.1021/ic3020332}}</ref>

==History==
The manganate(V) anion was first reported in 1946 by Hermann Lux, who synthesized the intensely blue sodium hypomanganate by reacting [[sodium oxide]] {{chem|Na|2|O}} and [[manganese dioxide]] {{chem|MnO|2}} in fused [[sodium nitrite]] {{chem|NaNO|2}} at 500 °C.<ref name=Lux>Herrman Lux (1946): "[http://zfn.mpdl.mpg.de/data/1/ZfN-1946-1-0281.pdf Über Salze des fünfwertigen Mangans]." ''Zeitschrift für Naturforschung'', volume 1, pages 281-283.</ref><ref name=Loye/>  He also crystalized the salt from strong (50%) [[sodium hydroxide]] solutions as the [[hydrate|decahydrate]] {{chem|Na|3|MnO|4}}·10{{chem|H|2|O}}.

==Structure and properties==
Manganate(V) is a tetrahedral [[oxyanion]] structurally similar to [[sulfate]], manganate, and permanganate.  As expected for a tetrahedral complex with a d<sup>2</sup> configuration, the anion has a [[triplet state|triplet]] ground state.<ref name=Loye>{{cite journal|author1=zur Loye, K. D. |author2=Chance, W. M. |author3=Yeon, J. |author4=zur Loye, H.-C. |title=Synthesis, Crystal Structure, and Magnetic Properties of the Oxometallates KBaMnO<sub>4</sub> and KBaAsO<sub>4</sub>|journal=Solid State Sciences|year=2014|volume=37|pages=86–90|doi=10.1016/j.solidstatesciences.2014.08.013|bibcode=2014SSSci..37...86Z|doi-access=free}}</ref>

The anion is a bright blue species<ref name="G&E">{{Greenwood&Earnshaw1st|pages=1221–22}}.</ref> with a visible absorption maximum at wavelength ''λ''<sub>max</sub>&nbsp;= 670&nbsp;nm (''ε'' = {{nowrap|900&nbsp;dm<sup>3</sup> mol<sup>−1</sup> cm<sup>−1</sup>}}).<ref name="JCS">{{citation | journal = J. Chem. Soc. | year = 1956 | pages = 3373–80 | doi =   10.1039/JR9560003373 | title = Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions | first1 = A. | last1 = Carrington | first2 = M. C. R. | last2 = Symons}}</ref><ref name="Mandelate">{{citation | title = 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 | first1 = Donald G. | last1 = Lee | first2 = Tao | last2 = Chen | journal = J. Am. Chem. Soc. | year = 1993 | volume = 115 | issue = 24 | pages = 11231–36 | doi = 10.1021/ja00077a023}}.</ref>

==Stability==
Hypomanganate is unstable towards [[disproportionation]] to [[manganate|manganate(VI)]] and [[manganese dioxide]]:<ref name="C&W">{{Cotton&Wilkinson4th|page=746}}.</ref><ref name="G&E"/>  The estimated [[electrode potential]]s at [[pH]]&nbsp;14 are:<ref>{{RubberBible62nd|page=D-134}}.</ref><ref>{{citation | title = Manganese – compounds – standard reduction potentials | url = http://www.webelements.com/manganese/compounds.html | publisher = WebElements | accessdate = 2010-06-26}}.</ref><ref name="Epot">{{citation | title = Rate of the MnO<sub>4</sub><sup>−</sup>/MnO<sub>4</sub><sup>2−</sup> and MnO<sub>4</sub><sup>2−</sup>/MnO<sub>4</sub><sup>3−</sup> electrode reactions in alkaline solutions at solid electrodes | first1 = K. | last1 = Sekula-Brzezińska | first2 = P. K. | last2 = Wrona | first3 = Z. | last3 = Galus | journal = Electrochim. Acta | volume = 24 | issue = 5 | pages = 555–63 | doi = 10.1016/0013-4686(79)85032-X | year = 1979}}.</ref>
:MnO{{su|b=4|p=2−}} + e<sup>−</sup> {{eqm}} MnO{{su|b=4|p=3−}}&nbsp;&nbsp;&nbsp;''E'' = +0.27 V
:MnO{{su|b=4|p=3−}} + e<sup>−</sup> + {{nowrap|2 H<sub>2</sub>O}} {{eqm}} MnO<sub>2</sub> + {{nowrap|4 OH<sup>−</sup>}}&nbsp;&nbsp;&nbsp;''E'' = +0.96 V
However, the reaction is slow in very alkaline solutions (with OH<sup>−</sup> concentration above 5–10 [[mole (unit)|mol]]/[[liter|L]]).<ref name="G&E"/><ref name=Lux/>

The disproportionation is believed to pass through a protonated intermediate,<ref name="Epot"/> with the [[acid dissociation constant]] for the reaction HMnO{{su|b=4|p=2−}}&nbsp;{{eqm}} MnO{{su|b=4|p=3−}}&nbsp;+ H<sup>+</sup> being estimated as p''K''<sub>a</sub>&nbsp;= {{nowrap|13.7 ± 0.2}}.<ref name=PulseRad>{{citation | title = Studies of Manganate(V), -(VI), and -(VII) Tetraoxyanions by Pulse Radiolysis. Optical Spectra of Protonated Forms | first1 = J. D. | last1 = Rush | first2 = B. H. J. | last2 = Bielski | journal = Inorg. Chem. | year = 1995 | volume = 34 | issue = 23 | pages = 5832–38 | doi = 10.1021/ic00127a022}}.</ref> However, K<sub>3</sub>MnO<sub>4</sub> has been cocrystallized with Ca<sub>2</sub>Cl(PO<sub>4</sub>), allowing the study of the [[Ultraviolet–visible spectroscopy|UV–visible spectrum]] of the hypomanganate ion.<ref name="C&W"/><ref>{{citation | journal = J. Chem. Soc. | year = 1956 | pages = 3373–80 | doi = 10.1039/JR9560003373 | title = Structure and reactivity of the oxy-anions of transition metals. Part I. The manganese oxy-anions | first1 = A. | last1 = Carrington | first2 = M. C. R. | last2 = Symons}}.</ref>

==Preparation==
Hypomanganates may be prepared by the careful reduction of manganates with [[sulfite]],<ref name="G&E"/> [[hydrogen peroxide]]<ref name="H2O2">{{citation | title = Oxidation of hydrocarbons. 18. Mechanism of the reaction between permanganate and carbon-carbon double bonds | first1 = Donald G. | last1 = Lee | first2 = Tao | last2 = Chen | journal = J. Am. Chem. Soc. | year = 1989 | volume = 111 | issue = 19 | pages = 7534–38 | doi =  10.1021/ja00201a039}}.</ref> or [[Mandelic acid|mandelate]].<ref name="Mandelate"/>

Hypomanganates can also be prepared by the solid state method under {{O2}} flow near 1000 °C.<ref name=Loye/><ref name=Dardenne/><ref name=Grisafe/> <ref name=Jiang/> They can be prepared also via low temperature routes such as hydrothermal synthesis or flux growth.<ref name=Loye/> It is produced by dissolving manganese dioxide in molten [[sodium nitrite]].<ref>{{cite journal|first=R. B. |last=Temple|author2=Thickett, G. W.|title=The formation of manganese(v) in molten sodium nitrite|journal=Australian Journal of Chemistry|date=1972|volume=25|page=55|doi=10.1071/CH9720655|issue=3|doi-access=free}}</ref>

==Uses==
The [[strontium vanadate fluoride]] {{chem|Sr|5|(|VO|4|)|3|F}} compound, with hypomanganate substituted for some [[vanadate]] units, has been investigated for potential use in near infrared lasers.<ref name=Merkle>L. D. Merkle, Y. Guyot, and B. H. T. Chai (1995): "Spectroscopic and laser investigations of Mn<sup>5+</sup>:Sr<sub>5</sub>(VO4)<sub>3</sub>F". ''Journal of Applied Physics'', volume 77, issue 2, pages 474-480. {{doi|10.1063/1.359585}}</ref>

The barium salt {{chem|Ba|3|(|MnO|4|)|2}} has interesting magnetic properties.<ref name=Stone>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 {{chem|Ba|3|Mn|2|O|8}}". ''Physics Review B'', volume 77, page 134406  {{doi|10.1103/PhysRevB.77.134406}}</ref>

==Related compounds==
In theory, hypomanganate would be the [[conjugate base]] of '''hypomanganic acid''' {{chem|H|3|MnO|4}}.  This acid cannot be formed because of its rapid disproportionation, but its third [[acid dissociation constant]] has been estimated by [[pulse radiolysis]] techniques:<ref name="PulseRad"/>
:HMnO{{su|b=4|p=2−}} {{eqm}} MnO{{su|b=4|p=3−}} + H<sup>+</sup>&nbsp;&nbsp;&nbsp;p''K''<sub>a</sub> = {{nowrap|13.7 ± 0.2}}

Cyclic [[ester]]s of hypomanganic acid are thought to be intermediates in the oxidation of [[alkene]]s by [[permanganate]].<ref name="Mandelate"/>

==See also==

* [[Dimanganite]], a manganate(III) anion {{chem|Mn|2|O|6|6-}}
* [[Manganate]] or manganate(VI), {{chem|MnO|4|2-}}
* [[Permanganate]] or manganate(VII), {{chem|Mn|O|4|-}}

==References==
{{reflist}}

[[Category:Manganese(V) compounds]]
[[Category:Transition metal oxyanions]]