Vanadate

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Orthovanadate anion.svg

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, VO43− 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[edit]

Some examples of discrete ions are

  • VO43− "orthovanadate", tetrahedral.[2]
  • V2O74− "pyrovanadate", corner shared VO4 tetrahedra similar to dichromate ion[2]
  • V3O93− cyclic with corner shared VO4 tetrahedra [4]
  • V4O124− cyclic with corner shared VO4 tetrahedra [5]
  • V5O143− corner shared VO4 tetrahedra [6]
  • V10O286− "decavanadate", edge and corner shared VO6 octahedra[2]
  • V12O324−[2]
  • V13O343− fused VO6 octahedra [7]
  • V18O4212−[8]

Some examples of polymeric “infinite” ions are

  • [VO3]nn in e.g. NaVO3, sodium metavanadate[2]
  • [V3O8]nn in CaV6O16[9]
Ammonium-metavanadate-chains-3D.png
V5O14 ball and stick.png
Decavanadate polyhedra.png
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[edit]

Dissolution of vanadium pentoxide in strongly basic aqueous solution gives the colourless VO43– 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; HVO42−, V2O74−
  • pH 4–9; H2VO4, V4O124−, HV10O285−
  • pH 2–4; H3VO4, H2V10O284−

References[edit]

  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. ^ a b c d e f g Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419. 
  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 V5O143− 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.