Vanadate

In chemistry, a vanadate is a compound containing an oxoanion of vanadium generally in its highest oxidation state of +5. The simplest vanadate ion is the tetrahedral, orthovanadate, VO3−
4 anion, which is present in e.g. sodium orthovanadate and in solutions of V₂O₅ in strong base (pH > 13 ^[1]). Conventionally this ion is represented with a single double bond, however this is a resonance form as the ion is a regular tetrahedron with four equivalent oxygen atoms.

Additionally a range of polyoxovanadate ions exist which include discrete ions and "infinite" polymeric ions.^[2] There are also vanadates, such as rhodium vanadate, RhVO₄, which has a statistical rutile structure where the Rh³⁺ and V⁵⁺ ions randomly occupy the Ti⁴⁺ positions in the rutile lattice,^[3] that do not contain a lattice of cations and balancing vanadate anions but are mixed oxides.

In chemical nomenclature when vanadate forms part of the name, it indicates that the compound contains an anion with a central vanadium atom, e.g. ammonium hexafluorovanadate is a common name for the compound (NH₄)₃VF₆ with the IUPAC name of ammonium hexafluoridovanadate(III).

Examples of vanadate ions

Some examples of discrete ions are

• VO3−
  4 "orthovanadate", tetrahedral.^[2]
• V
  2O4−
  7 "pyrovanadate", corner-shared VO₄ tetrahedra, similar to the dichromate ion^[2]
• V
  3O3−
  9, cyclic with corner-shared VO₄ tetrahedra^[4]
• V
  4O4−
  12, cyclic with corner-shared VO₄ tetrahedra^[5]
• V
  5O3−
  14, corner shared VO₄ tetrahedra^[6]
• V
  10O6−
  28 "decavanadate", edge- and corner-shared VO₆ octahedra^[2]
• V
  12O4−
  32^[2]
• V
  13O3−
  34, fused VO₆ octahedra ^[7]
• V
  18O12−
  42^[8]

Some examples of polymeric “infinite” ions are

• [VO₃]n−
  n in e.g. NaVO₃, sodium metavanadate^[2]
• [V₃O₈]n−
  n in CaV₆O₁₆^[9]

metavanadate chains	V5O14	decavanadate ion

In these ions vanadium exhibits tetrahedral, square pyramidal and octahedral coordination. In this respect vanadium shows similarities to tungstate and molybdate, chromium however has a more limited range of ions.

Aqueous solutions

Dissolution of vanadium pentoxide in strongly basic aqueous solution gives the colourless VO3−
4 ion. On acidification, this solution's colour gradually darkens through orange to red at around pH 7. Brown hydrated V₂O₅ precipitates around pH 2, redissolving to form a light yellow solution containing the [VO₂(H₂O)₄]⁺ ion. The number and identity of the oxyanions that exist between pH 13 and 2 depend on pH as well as concentration. For example, protonation of vanadate initiates a series of condensations to produce polyoxovanadate ions:^[2]

• pH 9–12; HVO2−
  4, V
  2O4−
  7
• pH 4–9; H
  2VO−
  4, V
  4O4−
  12, HV
  10O5−
  28
• pH 2–4; H₃VO₄, H
  2V
  10O4−
  28

Pharmacological properties

Vanadate is a potent inhibitor of certain plasma membrane ATPases, such as Na⁺/K⁺-ATPase and Ca²⁺-ATPase (PMCA). However, it does not inhibit other ATPases, such as SERCA (sarco/endoplasmic reticulum Ca²⁺-ATPase), actomyosin ATPase and mitochondrial ATPase.^[10][11] Aureliano, Manuel; Crans, Debbie C. (2009). "Decavanadate and oxovanadates: Oxometalates with many biological activities". Journal Inorganic Biochemistry 103: 536–546. doi:10.1016/j.jinorgbio.2008.11010.

References

1. Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5
2. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.
3. Wells A.F. (1984) Structural Inorganic Chemistry 5th edition Oxford Science Publications ISBN 0-19-855370-6
4. Hamilton E. E., Fanwick P.E., Wilker J.J. (2002). "The Elusive Vanadate (V₃O₉)³⁻: Isolation, Crystal Structure, and Nonaqueous Solution Behavior". J. Am. Chem. Soc. 124 (1): 78. doi:10.1021/ja010820r.
5. G.-Y. Yang, D.-W. Gao, Y. Chen, J.-Q. Xu, Q.-X. Zeng, H.-R. Sun, Z.-W. Pei, Q. Su, Y. Xing, Y.-H. Ling and H.-Q. Jia (1998). "[Ni(C₁₀H₈N₂)₃]2[V₄O₁₂]·11H₂O". Acta Crystallographica C 54 (5): 616. doi:10.1107/S0108270197018751.
6. V. W. Day, Walter G. Klemperer, O. M. Yaghi (1989). "A new structure type in polyoxoanion chemistry: synthesis and structure of the V
   5O3−
   14 anion". J. Am. Chem. Soc. 111 (12): 4518. doi:10.1021/ja00194a068.
7. Hou D., Hagen K.D., Hill C.L. (1992). "Tridecavanadate, [V₁₃O₃₄]³⁻, a new high-potential isopolyvanadate". J. Am. Chem. Soc. 114 (14): 5864. doi:10.1021/ja00040a061.
8. Müller A., Sessoli R., Krickemeyer E., Bögge H., Meyer J., Gatteschi D., Pardi L., Westphal J., Hovemeier K., Rohlfing R., Döring J, Hellweg F., Beugholt C., Schmidtmann M. (1997). "Polyoxovanadates: High-Nuclearity Spin Clusters with Interesting Host-Guest Systems and Different Electron Populations. Synthesis, Spin Organization, Magnetochemistry, and Spectroscopic Studies". Inorg. Chem. 36 (23): 5239. doi:10.1021/ic9703641.
9. Jouanneau, S.; Verbaere, A.; Guyomard, D. (2003). "On a new calcium vanadate: synthesis, structure and Li insertion behaviour". Journal of Solid State Chemistry 172: 116. Bibcode:2003JSSCh.172..116J. doi:10.1016/S0022-4596(02)00164-0.
10. Luo D., Nakazawa M., Yoshida Y., Cai J., Imai S. (2000). "Effects of three different Ca2+ pump ATPase inhibitors on evoked contractions in rabbit aorta and activities of Ca2+ pump ATPases in porcine aorta". General Pharmacology: The Vascular System 34 (3): 211–220. doi:10.1016/S0306-3623(00)00064-1.
11. Bowman B.J., Slayman C.W. (1979). "The Effects of Vanadate on the Plasma Membrane ATPase of Neurospora crassa". Journal of Biological Chemistry 254 (8): 2928–2934.