Superconductivity Chevrel phases

Much of the interest in clusters of this type arises from their structural similarity to the fundamental structural element of the superconducting Chevrel phases M MogEg (M = Pb, Sn, Cu, etc.) and more recently discovered rhenium halco halide phases. Although these solid-state compounds are known only for Mo and Re, molecular MgEgLg clusters of Zr, V, Cr, Mo, W, Re, Fe, and Co have been reported (Table 2). The lone examples of octahedral zirconium- and vanadium-chalcogenide clusters are unique in that they also possess interstitial O and S atoms, respectively. Evidence for interstitial FI atoms in the clusters [Cr6Eg(PEt3)g] (E = S, Se) has been presented. ... 

R. Chevrel, M. Hirrien, M. Sergent - Superconducting Chevrel Phases ... 

In passing, it should be noted that Michel and Raveau had carried out electrical measurements on several alkaline-earth substituted La2Cu04 compounds and presented (140) their experimental results in a comprehensive review during 1984. Their work, however, was primarily structural with a focus on electrical and magnetic properties above 50 K for this reason they missed observing the superconducting transition at 30 K. It is this author s belief that these Cu-O phases should be called the "Raveau-Michel" phases in much the same way as the molybdenum sulfide superconductors are called the "Chevrel" phases. 

The superconductivity of the Chevrel phases MxMo6E8 has been attributed mainly to Mo6E8 cluster units, and Mt influences the critical... 

In the area of technological application there are two major topics the (real or postulated) involvement of metal atom clusters in catalysis and the remarkable superconducting properties of the Chevrel phases. The former topic has been abundantly covered in current review literature (54), although there are cautions to be recognized (55), and will not be further discussed here. Even the Rh2 + complexes have been reported to be catalytically active. Thus, Rh2(02CCF3)i, exhibits catalytic activity, toward cyclopropanation of alkenes with alkyl... 

The Chevrel phases have aroused great interest because they display remarkable superconductivity, as well as some other notable physical properties. Their superconductivity is exceptional in its persistence in the presence of magnetic fields, a property that is obviously important if superconductivity is to be exploited in making powerful magnets. In recent years a great many chemical variations on the basic MrMofiXs composition have been devised, for example, compounds such as Mo6Br6S3, which contains Mo6(ju3-Br)4(ju,3-S)4 units. 

In these compounds, as in the mixed valence copper sulfides,the nonmetallic moiety is the mixed valent species. Superconductivity also is known with the sulfides in the Chevrel Phases. In 1991, the pure fullerene phase of carbon,... 

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