Tantalum chloride clusters

The electrochemical behavior of Nb(V) in oxide free basic aluminum chloride -methyl-3-ethylimidazolium chloride - is reported to involve four reduction steps, but reduction to the free metal could not be achieved [1, 2]. Niobium and tantalum chloride cluster cores of the type [M6C1i2] (M=Nb or Ta) in this same ionic liquid have been studied in detail by electrochemical and spectroscopic methods and their behavior compared with the behavior of these systems in an MeCN electrolyte. Four reversible redox states are observed in the span z = 2-5 [3, 4]. 

Oxidized, metastable clusters are obtained for both families via solution processes near room temperature and, in parallel, these contain 14-e niobium and tantalum members, but 12-e (and 13-e) zirconium chloride clusters. Rare-earth-metal clusters don t provide such persuasive evidence small main-group Z examples are rather scarce but similar (12-14-e for R7X-12Z), while iodides centered by large metals cover a sizable range (16-20), as was rationalized earlier (see 5). 

Clusters of six molybdenum, niobium, or tantalum atoms have been known for muny years, predating the work with rhenium. There two types In the first, an octahedron of six metal atoms is coordinated by eight chloride ligands, one on each face of the octahedron (Fig. 16.64a). This is found in molybdenum dichloride, MoftCI,2. better formulated as [MoftCIg]CI4. Each Mo(II) atom can use its four electrons to form four bonds with adjacent molybdenum atoms and can receive dative bonds from the four chloride ligands 164... 

Metal cluster complexes were proposed to introduce mainly transition metals between the clay layers. Niobium, tantalum and molybdenum chlorides were exchanged on the clay surface and oxidized at 513 K under vacuum to transform... 

The scientific community did not realize the importance of cluster compounds for nearly 40 years after their discovery. In the early 1900s tantalum halides of the general formula [Ta6Xi2] + were being prepared. In 1907 the chloride was incorrectly reported as TaCb. In 1910 the... 

Mild oxidant agents often permit oxidations with retention of the cluster structures. One example of this kind of simple chemical electron-transfer reactions are the oxidations of niobium and tantalum clusters [M6Xi2] to the species with charges 3+ and 4+. The reaction with iron(III) chloride and cerium (IV) salts leads directly to the cations [M6Xi2] . ... 

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