Niobium oxychlorides

I 6 Titanium Niobium Oxychlorides Ligand Combination Strategy... 

When the niobium oxychloride clusters contain four oxygen ligands as inner ligands, different types of 2D cluster frameworks have been obtained. Their structures are briefly described below. 

I 6 Titanium Niobium Oxychlorides Ligand Combination Strategy [AsCTijCl,)] [(Nb6Cli204)3(Ti3Cl4)2] NbvSzIis... 

Summary of Crystallographic Data on Titanium Niobium Oxychlorides 93... 

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). 

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). 

Fig. 6.11 Space-filling views of the structures of niobium oxychlorides showing the trend of anion segregation.

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... 

Table 6.4 Number of valence electrons per cluster in niobium oxychlorides.

The use of both 8(CH3) values and iftM- H) magnitudes does, however, allow determination of the coordination mode in many instances (e.g., 462). Problems due to ligand dissociation are frequently evident in H-NMR studies of sulfoxide complexes. Thus the dimethyl sulfoxide adduct of niobium oxychloride (409) undergoes solvolysis in acetoni-... 

Niobium Oxychlorides.—The most important niobium oxy-chlorine compound is niobium oxytrichloride, NbOCl8, which is described below. 

Other nitrides of niobium of doubtful composition have been obtained by the action of ammonia on niobium pentoxide,4 niobium oxychloride 5 and niobium pentachloride. 

Lorine, D. J., Stevenson, F. D. Separation of niobium oxychloride from niobium pentachloride in a gas chromatograph by temperature programming. J. Chromatog. 

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