Chevrel compounds

The electronic structure of Chevrel compounds is similar to that in Fig. 7.3(a), but with different numbers of states in the upper and lower bands. Mo-Mo bonds split the d states into two bands (Nohl, Klose and Andersen, 1982). The lower band contains 24 states per MogSeg cluster, because there are 12 Mo-Mo bonds in each cluster (the 12 edges of the Mog octahedron). Each Mo contributes six electrons to the bands, for a... 

Chevrel compounds of the general formula A MogSg with A = Cu, Pb, La etc. are difficult to prepare in very pure state by the ceramic procedure. A one-step reduction of a precursor sulphide has been found to yield these phases (Nanjundaswamy et al, 1987) ... 

Fig. 16.67 Siructure of one of the Chevrel compounds. PbMo Ss. ( ) Mo (O) S (O) Pb [From Cotton. F. A. In Reactivity of Metal-Metal Bonds-, Chisholm, M. H., Ed. ACS Symposium Series 155 American Chemical Society Washington, DC 1981. Reproduced with permission.]...

Chevrel compounds of general formula ArM06S8 with A= Cu, Pb, La etc. (Fig. 5) are generally prepared by the ceramic method. A novel precursor compound has been employed [22] to obtain these compounds by a one-step reduction as given by the reaction ... 

Fig. 5. Structure of Chevrel compounds, A,Mo6Ch8 (Ch = S, Se, Te) (a) Mo, Chg building block, (b) structure of Chevrel compounds where the A cation is shown by the closed circle.

Figure 4. Structure of one of the Chevrel compounds PbMo6Ss. This drawing was kindly supplied by M. J. Sienko of Cornell University. ((%) Mo (O) S ( ) Pb)...

Figure 16-21 The idealized structure of a representative Chevrel compound.

The chemical and physical properties of the Chevrel compounds have been covered in books. [228] The enormous interest in these compounds was due to the fact that Mo6SgPb turned out to be a superconductor (7 = 14K), [229] with the highest upper critical fields, 60 Tesla, known at the time. 

Ternary chalcogenides, M MoeXs (M = a transition metal, rare earth, etc. and X = S, Se, or Te) a class of ORR active materials, were for the first time synthesized by Chevrel et al. [167] and are referred as Chevrel compounds. These complex chalcogenides have a central octahedral metal cluster wherein the delocalization of the electrons leads to high electronic conductivity and these clusters act as a reservoir for electronic charge carriers. The substitution of Mo atoms by other transition metal atoms causes an alteration in the position of the Fermi level in such a way that it is suitable for the redox potential of the O2/H2O [19] couple. 

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