Sodium decavanadate explained

Sodium decavanadate describes any member of the family of inorganic compounds with the formula Na6[V<sub>10</sub>O<sub>28</sub>](H2O)n. These are sodium salts of the orange-colored decavanadate anion [V<sub>10</sub>O<sub>28</sub>]6−.[1] Numerous other decavanadate salts have been isolated and studied since 1956 when it was first characterized.[2]

Preparation

The preparation of decavanadate is achieved by acidifying an aqueous solution of ortho-vanadate:[1]

10 Na3[VO<sub>4</sub>] + 24 HOAc → Na6[V<sub>10</sub>O<sub>28</sub>] + 12 H2O + 24 NaOAc

The formation of decavanadate is optimized by maintaining a pH range of 4–7. Typical side products include metavanadate, [VO<sub>3</sub>], and hexavanadate, [V<sub>6</sub>O<sub>16</sub>]2−, ions.[1]

Structure

The decavanadate ion consists of 10 fused VO6 octahedra and has D2h symmetry.[3] [4] [5] The structure of Na6[V<sub>10</sub>O<sub>28</sub>]·18H2O has been confirmed with X-ray crystallography.[6]

The decavanadate anions contains three sets of equivalent V atoms (see fig. 1).[3] These include two central VO6 octahedra (Vc) and four each peripheral tetragonal-pyramidal VO5 groups (Va and Vb). There are seven unique groups of oxygen atoms (labeled A through G). Two of these (A) bridge to six V centers, four (B) bridge three V centers, fourteen of these (C, D and E) span edges between pairs of V centers, and eight (F and G) are peripheral.

The oxidation state of vanadium in decavanadate is +5.

Acid-base properties

Aqueous vanadate (V) compounds undergo various self-condensation reactions.[7] Depending on pH, major vanadate anions in solution include VO2(H2O)42+, VO43−, V2O73−, V3O93−, V4O124−, and V10O286−. The anions often reversibly protonate.[5] Decavanadate forms according to this equilibrium:[2] [7]

H3V10O283− ⇌ H2V10O284− + H+

H2V10O284− ⇌ HV10O285− + H+

HV10O285−(aq) ⇌ V10O286− + H+

The structure of the various protonation states of the decavanadate ion has been examined by 51V NMR spectroscopy.[5] [7] Each species gives three signals; with slightly varying chemical shifts around −425, −506, and −523 ppm relative to vanadium oxytrichloride; suggesting that rapid proton exchange occurs resulting in equally symmetric species.[8] The three protonations of decavanadate have been shown to occur at the bridging oxygen centers, indicated as B and C in figure 1.[8]

Decavanadate is most stable in pH 4–7 region.[1] [4] [7] Solutions of vanadate turn bright orange at pH 6.5, indicating the presence of decavanadate. Other vanadates are colorless. Below pH 2.0, brown V2O5 precipitates as the hydrate.[3] [7]

V10O286− + 6H+ + 12H2 ⇌ 5V2O5

Potential uses

Decavanadate has been found to inhibit phosphoglycerate mutase, an enzyme which catalyzes step 8 of glycolysis. In addition, decavandate was found to have modest inhibition of Leishmania tarentolae viability, suggesting that decavandate may have a potential use as a topical inhibitor of protozoan parasites.[9]

Related decavanadates

Many decavanadate salts have been characterized. NH4+, Ca2+, Ba2+, Sr2+, and group I decavanadate salts are prepared by the acid-base reaction between V2O5 and the oxide, hydroxide, carbonate, or hydrogen carbonate of the desired positive ion.[1]

6 NH3 + 5 V2O5 + 3 H2O ⇌ (NH4)6[V<sub>10</sub>O<sub>28</sub>]

Other decavanadates:

(NH4)6[V<sub>10</sub>O<sub>28</sub>]·6H2O[2]

K6[V<sub>10</sub>O<sub>28</sub>]·9H2O[2]

K6[V<sub>10</sub>O<sub>28</sub>]·10H2O[1] [2] [3]

Ca3[V<sub>10</sub>O<sub>28</sub>]·16H2O[2] [3]

K2Mg2[V<sub>10</sub>O<sub>28</sub>]·16H2O[2] [3]

K2Zn2[V<sub>10</sub>O<sub>28</sub>]·16H2O[1] [2] [3]

Cs2Mg2[V<sub>10</sub>O<sub>28</sub>]·16H2O[3]

Cs4Na2[V<sub>10</sub>O<sub>28</sub>]·10H2O[10]

K4Na2[V<sub>10</sub>O<sub>28</sub>]·16H2O[11]

Sr3[V<sub>10</sub>O<sub>28</sub>]·22H2O[10]

Ba3[V<sub>10</sub>O<sub>28</sub>]·19H2O[10]

[(C<sub>6</sub>H<sub>5</sub>)<sub>4</sub>P]H3V10O28·4CH3CN[8]

Ag6[V<sub>10</sub>O<sub>28</sub>]·4H2O[12] [13] Naturally occurring decavanadates include:

Ca3V10O28·17 H2O (Pascoite)

Ca2Mg(V10O28)·16H2O (Magnesiopascoite)

Na4Mg(V10O28)·24H2O (Huemulite)

Notes and References

  1. Book: Johnson, G. . Murmann, R. K. . Sodium and Ammonium Decayanadates(V) . Inorganic Syntheses. 1979 . 19. 140–145. 10.1002/9780470132500.ch32. 978-0-471-04542-7 .
  2. Rossotti, F. J. . Rossotti, H. . Equilibrium Studies of Polyanions. Acta Chemica Scandinavica. 1956. 10. 957–984. 10.3891/acta.chem.scand.10-0957. free.
  3. Evans, H. T. Jr . The molecular structure of the isopoly complex ion, decavanadate. Inorg. Chem.. 1966. 5. 967–977. 10.1021/ic50040a004.
  4. Book: Kustin, K. . Pessoa, J. C. . Crans, D. C. . Vandadium: The Versatile Metal. 2007. American Chemical Society. Washington, D. C.. 978-0-8412-7446-4.
  5. Book: Rehder, D. . Bioinorganic Vanadium Chemistry. 2008. Wiley & Sons. 13–51. 978-0-470-06509-9.
  6. Durif, P.A. . Averbuch-pouchot, M.T. . Structure d'un Décavanadate d'Hexasodium Hydraté. Acta Crystallogr. B . 1980. 36. 3. 680–682. 10.1107/S0567740880004116. 1980AcCrB..36..680D .
  7. Book: Tracey, A.S. . Vanadium Compounds . Crans, D.C. . 1998 . American Chemical Society . Washington D.C. . 0-8412-3589-9 .
  8. Day, V. W. . Walter G. Klemperer . Klemperer, W. G. . Maltbie, D. J. . Where Are the Protons in H3V10O283−?. Journal of the American Chemical Society. 1987. 109. 10. 2991–3002. 10.1021/ja00244a022.
  9. Turner . Timothy . Nguyen . Victoria . McLauchlan . Craig . Dymon . Zaneta . Dorsey . Benjamin . Hooker . Jaqueline . Jones . Marjorie . Inhibitory effects of decavanadate on several enzymes and Leishmania tarentolae In Vitro . Journal of Inorganic Biochemistry . March 2012 . 108 . 96–104 . 10.1016/j.jinorgbio.2011.09.009 . 22005446 . 23 January 2021.
  10. Dametto, A.C. . de Arauju, A.S. . de Souza Correa, R. . Guilherme, L.R. . Massabni, A.C. . Synthesis, infrared spectroscopy and crystal structure determination of a new decavanadate. J Chem Crystallogr. 2010. 40. 11. 897–901. 10.1007/s10870-010-9759-x. 97736357.
  11. Matias, P.M. . Pessoa, J.C. . Duarte, M.T. . Maderia, C. . Tetrapotassium disodium decavanadate(V) decahydrate. Acta Crystallogr. C. 2000. 57. 3. e75–e76. 10.1107/S0108270100001530. 15263200. 2000AcCrC..56E..75M .
  12. Escobar, M.E. . Baran, E.J. . Die Schwingungsspektren einiger kristalliner Dekavanadate. Monatshefte für Chemie. 1981. 112. 43–49. 10.1007/BF00906241. 101366009.
  13. Aureliano . Manuel . Crans . Debbie C. . 2009 . Decavanadate and oxovanadates: Oxometalates with many biological activities . . 103 . 4 . 536–546 . 10.1016/j.jinorgbio.2008.11.010 . 19110314 . 0162-0134.