Sodium decavanadate describes any member of the family ofinorganic compounds with the formula Na6[V10O28](H2O)n. These aresodium salts of the orange-colored decavanadateanion [V10O28]6−.[1] Numerous other decavanadate salts have been isolated and studied since 1956 when it was first characterized.[2]
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]
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 withX-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.
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 V10O286−. The anions often reversiblyprotonate.[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 by51V NMR spectroscopy.[5][7] Each species gives three signals; with slightly varyingchemical shifts around −425, −506, and −523 ppm relative tovanadium 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]
Decavanadate has been found to inhibitphosphoglycerate mutase, anenzyme which catalyzes step 8 ofglycolysis. In addition, decavandate was found to have modest inhibition ofLeishmania tarentolae viability, suggesting that decavandate may have a potential use as a topicalinhibitor of protozoan parasites.[9]
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]
^abcdeTracey, A.S.; Crans, D.C. (1998).Vanadium Compounds. Washington D.C.: American Chemical Society.ISBN0-8412-3589-9.
^abcDay, 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.
^abcDametto, 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.S2CID97736357.
