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
CAS Number	12315-57-0^N
Properties
Chemical formula	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 D_2h 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 (V_c) and four each peripheral tetragonal-pyramidal VO₅ groups (V_a and V_b). 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

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[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
    ₁₀O⁶⁻
    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.