Sodium decavanadate

Sodium decavanadate describes any member of the family of inorganic compounds with the formula Na6[V10O28](H2O)n. These are sodium salts of the orange-colored decavanadate anion [V10O28]6−.[1] Numerous other decavanadate salts have been isolated and studied since 1956 when it was first characterized.[2]

Sodium decavanadate
Identifiers
Properties
Na6[V10O28]
Molar mass 1419.6 g
Appearance orange solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N (what is YN ?)
Infobox references

Preparation

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

10 Na3[VO4] + 24 HOAc → Na6[V10O28] + 12 H2O + 24 NaOAc

The formation of decavanadate is optimized by maintaining a pH range of 4–7. Typical side products include metavanadate, [VO3]−, and hexavanadate, [V6O16]2−, ions.[1]

Structure

The decavanadate ion consists of 10 fused VO6 octahedra and has D2h symmetry.[3][4][5] The structure of Na6[V10O28]·18H2O has been confirmed with X-ray crystallography.[6]

Figure 1: structure of decavanadate ion with equivalent V and O atoms indicated

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 V10O266−. 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

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[V10O28]

Other decavanadates:

(NH4)6[V10O28]·6H2O[2]
K6[V10O28]·9H2O[2]
K6[V10O28]·10H2O[1][2][3]
Ca3[V10O28]·16H2O[2][3]
K2Mg2[V10O28]·16H2O[2][3]
K2Zn2[V10O28]·16H2O[1][2][3]
Cs2Mg2[V10O28]·16H2O[3]
Cs4Na2[V10O28]·10H2O[9]
K4Na2[V10O28]·16H2O[10]
Sr3[V10O28]·22H2O[9]
Ba3[V10O28]·19H2O[9]
[(C6H5)4P]H3V10O28·4CH3CN[8]
Ag6[V10O28]·4H2O[11][12]

Naturally occurring dewcavanadates include:

Ca3V10O28·17 H2O (Pascoite)
Ca2Mg(V10O28)·16H2O (Magnesiopascoite)
Na4Mg(V10O28)·24H2O (Huemulite)

References
  1. Johnson, G.; Murmann, R. K. (2007). Sodium and Ammonium Decavanadates. Inorganic Syntheses. 19. pp. 140–145. doi:10.1002/9780470132500.ch32.CS1 maint: uses authors parameter (link)
  2. Rossotti, F. J.; Rossotti, H. (1956). "Equilibrium Studies of Polyanions". Acta Chemica Scandinavica. 10: 957–984. doi:10.3891/acta.chem.scand.10-0957.CS1 maint: uses authors parameter (link)
  3. Evans Jr., H. T. (1966). "The molecular structure of the isopoly complex ion, decavanadate". Inorg. Chem. 5: 967–977. doi:10.1021/ic50040a004.CS1 maint: uses authors parameter (link)
  4. Kustin, K.; Pessoa, J. C.; Crans, D. C. (2007). Vandadium: The Versatile Metal. Washington, D. C.: American Chemical Society. ISBN 978-0-8412-7446-4.CS1 maint: uses authors parameter (link)
  5. Rehder, D. (2008). Bioinorganic Vanadium Chemistry. Wiley & Sons. pp. 13–51. ISBN 978-0-470-06509-9.CS1 maint: uses authors parameter (link)
  6. Durif, P.A.; Averbuch-pouchot, M.T. (1980). "Structure d'un Décavanadate d'Hexasodium Hydraté". Acta Crystallogr. B. 36 (3): 680–682. doi:10.1107/S0567740880004116.CS1 maint: uses authors parameter (link)
  7. Tracey, A.S.; Crans, D.C. (1998). Vanadium Compounds. Washington D.C.: American Chemical Society. ISBN 0-8412-3589-9.
  8. Day, V. W.; Klemperer, W. G.; Maltbie, D. J. (1987). "Where Are the Protons in H3V10O283−?". Journal of the American Chemical Society. 109 (10): 2991–3002. doi:10.1021/ja00244a022.CS1 maint: uses authors parameter (link)
  9. Dametto, A.C.; de Arauju, A.S.; de Souza Correa, R.; Guilherme, L.R.; Massabni, A.C. (2010). "Synthesis, infrared spectroscopy and crystal structure determination of a new decavanadate". J Chem Crystallogr. 40 (11): 897–901. doi:10.1007/s10870-010-9759-x.CS1 maint: uses authors parameter (link)
  10. Matias, P.M.; Pessoa, J.C.; Duarte, M.T.; Maderia, C. (2000). "Tetrapotassium disodium decavanadate(V) decahydrate". Acta Crystallogr. C. 57 (3): e75–e76. doi:10.1107/S0108270100001530. PMID 15263200.CS1 maint: uses authors parameter (link)
  11. Escobar, M.E.; Baran, E.J. (1981). "Die Schwingungsspektren einiger kristalliner Dekavanadate". Monatshefte für Chemie. 112: 43–49. doi:10.1007/BF00906241.CS1 maint: uses authors parameter (link)
  12. Aureliano, Manuel; Crans, Debbie C. (2009). "Decavanadate (V
    10    O6−
    28    ) and oxovanadates: Oxometalates with many biological activities"    . Journal of Inorganic Biochemistry. 103 (4): 536–546. doi:10.1016/j.jinorgbio.2008.11.010. ISSN 0162-0134.
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