Niobium oxide clusters

Overview of the Chemistry of Niobium Chloride and Niobium Oxide Cluster Compounds 83... 

A growing chemistry of niobium oxide clusters continues to emerge. The reduced niobates and the NbO suboxide are also built up from condensation of Me units through shared vertices, namely, Nb60i2. Although the inner halides within the [MeXi2] + core are relatively inert to substitution, Nbe and Tae oxohalides, such as [Nb6Cli2-mOm]"+ m = 1 —4) and... 

As a specific example of the correlations we have observed, our experimental results demonstrate that the reactions of vanadium and niobium oxide cluster cations with methanol lead to dehydrogenation of methanol under single collision conditions producing neutral formaldehyde [16]. Formaldehyde is, indeed, a major product formed from methanol over condensed-phase vanadia surfaces [17]. Another study conducted in our laboratory showed that,, Clj products were formed during the reaction between certain clusters and CCl, leaving phosgene (COClj) as the most likely neutral product [15, 18]. The decomposition of... 

In contrast to chloride compounds, niobium oxides have a VEC of 14 electrons, due to an overall anti-bonding character of the a2u state, caused by a stronger Nb-O anti-bonding contribution. In some cases, the VEC cannot be determined unambiguously due to the uncertainty in the electron distribution between the clusters and additional niobium atoms present in the majority of the structures. The 14-electron compounds exhibit semiconducting properties and weak temperature-independent paramagnetism. Unlike niobium chlorides, the oxides do not exhibit a correlation between the electronic configuration and intra-cluster bond distances. 

The number of valence electrons in niobium oxychloride clusters decreases as the number of oxide hgands increases (Table 6.4). The compound Cs2LuNbi Cli70 has the VEC of 16 as found in most chloride clusters, suggesting that the presence of one oxide ligand per cluster does not tip the balance between the Nb-Nb bonding and Nb-L anti-bonding contributions to the a2u state. The VEC of most clusters... 

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... 

The structural chemistry described in Section 5.3 is concerned with reduced niobium oxides in which various NbeOu clusters are discernible. - Phases with ordered structures have been prepared by careful choice of preparative conditions. Reduced niobium oxides have NbeOn cluster cores which are discrete (OD) or linked together through apical oxygen atoms to form ID (chain), 2D (layer), or 3D... 

The alkali metal rhenium- and technetium chalcogenide clusters described in Section 5.6 are also octahedral.These clusters have M6Es units with eight face-capping anions on the octahedral faces in contrast to the niobium halide or oxide clusters. The A4M6S14 (A = alkali metal, M — Re, Tc), Cs6Rc6Si2, and... 

Discrete and Condensed Clusters in Low Valent Niobium Oxides... 

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