Vanadato

En química, un vanadato es un compuesto que contiene un oxianión de vanadio en su estado de oxidación más alto, +5. El ion vanadato más simple es el anión ortovanadato VO₄³⁻, tetrahedro, el cual está presente, por ejemplo, en el ortovanadato de sodio y en soluciones de pH > 13^[1] ). Convencionalmente este ion es representado con un enlace doble sencillo, sin embargo esta es una forma de resonacia ya que el ion es un tetrahedro regular con cuatro átomos de oxígeno equivalentes.

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(V).

Ejemplos de iones vanadato

Algunos ejemplos de iones discretos son

• VO₄³⁻ "ortovanadato", tetrahedral.^[2]
• V₂O₇⁴⁻ "pirovanadato", ángulo compartido VO₄ tetrahedra similar to dichromate ion^[2]
• V₃O₉³⁻ cíclico con ángulo compartido 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]
• V₁₂O₃₂^4−[2]
• V₁₃O₃₄³⁻ Octahedro VO₆ fundido^[7]
• V₁₈O₄₂^12−[8]

Algunos ejemplos de iones poliméricos "infinitos" son

• [VO₃]_nⁿ⁻ en e.j. NaVO₃, metavanadato de sodio^[2]
• [V₃O₈]_nⁿ⁻ en 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 W and Mo, chromium however has a more limited range of ions.

Solución acuosa

Dissolution of vanadium pentoxide in strongly basic aqueous solution gives the colourless VO₄^3– 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 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⁻

Referencias

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, A. (1997), Chemistry of the Elements (2nd ed.), Oxford: 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):  pp. 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 Section C Crystal Structure Communications 54:  pp. 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:  pp. 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:  pp. 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:  pp. 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:  pp. 116. doi:10.1016/S0022-4596(02)00164-0.