Protonation of the decavanadate(6–) ion: a vanadium-51 nuclear magnetic resonance study

Abstract

The first protonation site of [Vlo02,]6differs both from the second protonation site and from the site of preferential interaction with aqueous manganese(i1) ion. It is probably an out-of-plane apex, and not a bridging oxygen as has recently been proposed. The 61V n.m.r. linewidths are almost independent of direct protonation but depend in-Coventry CV4 7AL directly on more distant protonation. THE isopolyvanadate ion [Vl,02,]6-has the structure shown in Figure 1 in all the crystals in which it has so far Q f FIGURE 1 Crystal structure of [Vl0O2.J6-(refs. 1 and 2)been identified.1.2 Recently, high-field 51V n.m.r. studies 3 9 4 have greatly improved upon early derivativemode n.m.r. studies5'6 and have confirmed that the 4 : 4 : 2 population ratio of three distinct vanadium-atom types, present in the solid, also persists in solution. However, the pH dependence of these resonances has not yet been studied in any detail. Conventional pH studies of this system ' 9 , have not been easy because of its metastability and sensitivity to ionic strength and counter ion. However, they show successive pKa values in the ranges pK, 5.5-6.0, pK2 3.1-3.7, and pK3 z 2. At pH < 2 the ion hydrolyses fairly rapidly to give [V02(OH2),]+,g and at pH < 6.5 it hydrolyses slowly to give various tetrahedral specie^.^^^^ Vanadium41 n.m.r. spectra should give additional information about the separate protonation sites, and should be less sensitive than conventional pH studies to the system's metastability.Polyoxoanions are generally believed to protonate at terminal oxygens, and therefore some workers have

Vanadium distribution, lipid peroxidation and oxidative stress markers upon decavanadate in vivo administration

“…Since most of the vanadate species can be detected by 51 V NMR spectroscopy, it was observed that the spectra of decavanadate stock solution, 50 mM in total vanadium, at pH 7.0, contained mainly decameric species once the three signals from decameric vanadate species, ascribed to the three vanadium atoms of the decavanadate structure [28], are observed: V10A at À517 ppm, V10B at À501 ppm, V10C at À426 ppm and a weak signal (V1) at À562 ppm (Fig. 1A).…”

The pseudo-orthorhombic structure of caesium dihydrogendecavanadate tetrahydrate

“…Klemperer & Shum (1977) and Howarth & Jarrold (1978) have determined the protonation sites of (H2VI0028) 4-in solution using 170 NMR and 5W NMR spectroscopy, respectively. The former authors found that Ob and Od type (see Table 2) are the most basic oxygens, Ob being more basic than Od, while the latter authors pointed out that the most probable protonation sites are at the apical oxygens Of and Og.…”

Reaction Dynamics of the Decaniobate Ion [HxNb10O28](6−x)− in Water

“…6.6. Furthermore, another m 2 -O site (E) is extraordinarily slow to exchange (Figure 1 c) [2,3] with pK x values of: pK 1 = 6.0; pK 2 = 3.74, and pK 3 = 1.6 (I = 0.6 m). Using these equilibrium constants, the [Nb 10 O 28 ] 6À species dominates at most pH conditions of this study, with the monoprotonated form [HNb 10 O 28 ]…”