Vanadium cluster ions

The reactions of the vanadium oxide cluster cations with CCI4 were of three types (248). The small cluster ions reacted by transfer of a chloride ion. The larger clusters starting with the V4OJ+ series reacted by the addition of a chlorine atom to the cluster or the loss of one oxygen atom and the addition of two chlorine atoms. 

A reaction of particular relevance with respect to applied catalysis is the oxidative dehydrogenation (ODH) of hydrocarbon by VmOn ions according to reaction 2, which involves a two-electron reduction of the cluster. By means of a systematic study of the reactions of various YmOn ions as well as the related oxo-vanadium hydroxides VmO H+ ions with a set of C4-hydrocarbons, it was demonstrated recently that the ODH activity of the cluster ions shows a clear correlation with the formal valence of vanadium in the cluster ions with a maximum reactivity for formal vanadium (V) (Fig. 3) [84]. In such a kind of reactivity screening, it is essential to include more than a single reagent as a probe for the reactivity of the different ions in order to reduce interferences by kinetic barriers of one particular combination of neutral and ionic reactants [85]. Accordingly, the sums of the relative rate constants for the ODH reactions of the four different butenes are considered and normalized to the most reactive ion studied, which turns out to be the formally pure vanadium (V) compoimd In addition to isomeric... 

Stein et al. and Janauer et al. have synthesized layered mesostructured materials of (C,9H42N)6(H2W,204o) and [Ci2H25N(CH3)3]6(H2Wi2O40), respectively [2,8]. These materials are of great interest because their walls are made of cluster anions, in contrast to the amorphous walls of the other materials. The tungsten, vanadium, niobium, and molybdenum oxide precursors reacting with cationic surfactants, often form similar cluster ion salts with lamellar structures [2]. 

In addition to bulk material, vanadium oxide cluster ions, such as V20(4.e/, V30(6 8), V40(8-ii/, VsOdi.n), V60(i3.i5), and V70(i6.i8)" [78, 79], can be prepared in gas phase. The chemical reactivity of these species shows a distinct dependence on cluster size. While the smaller clusters are reacting quite easily with other molecules, the reactivity of the larger systems is decreased with the exception of oxygen-rich clusters, which can release molecular oxygen upon collision with reactant gas. 

Zemski KA, Justes DR, Bell RC, Castleman AW Jr (2001) Reactions of niobium and tantalum oxide cluster cations and anions with n-butane. J Phys Chem A 105 4410 Bell RC, Castleman AW Jr (2002) Reactions of vanadium oxide cluster ions with 1, 3-butadiene and isomers of butane. J Phys Chem A 106 9893... 

Assuming that the concentration of isolated vanadium particles does not change upon increasing the vanadium content in the graft layer, one can evaluate the proportion of isolated and cluster ions as a function of the vanadium surface density... 

Although the trinuclear core formally contains vanadium(lll) and vanadium (IV) ions, all are equivalent suggesting that the unpaired electron(s) are delocalized. The paramagnetic trimetallic center also has an unusual effect on the chemical shifts of a-protons of the dithiocarbamate ligands in the NMR spectrum, which can be shifted downfield as far as 6 10.7 ppm. The clusters are redox active and undergo reversible one-electron reduction and oxidation processes (697). 

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