Niobium Oxychloride Cluster Compounds

Investigations of the interaction between 3d transition metals and octahedral halide or oxide metal clusters led to the preparation of a number of novel cluster compounds such as the series AxByNbgClig (A = Li, K, Rb, Cs B=Ti, V, Mn, Cu) [33], and TizNbgOu [34]. 

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Table 6.3 Ligand arrangement and structural properties in reported niobium oxychloride cluster compounds.

Trivalent cations are present in most of niobium oxychloride cluster compounds known to date and play an important role in their structural chemistry. The series AxNb6Cli202 (A = K, Rb, Cs, In), on the other hand, represents an example of an oxychloride structure stabilized without a trivalent counter-ion (Fig. 6.12). 

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... 

The structural features of most niobium oxychlorides known to-date are summarized in Table 6.1. The use of a combination of chloride and oxide hgands leads to compounds with unique structure types [41], characterized by a remarkable variety of cluster frameworks, ranging from discrete cluster units to chains, layers, and three-dimensional nets, some topologies of which are unprecedented in compounds containing octahedral clusters. Most of the niobium oxychlorides known to date have anisotropic structures (the exceptions are Cs2LuNb,5Cli70 and PbLusNbsClisOg). 

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