Roger CHEVREL

Laboratoire de Chimie du Solide at Inorganique Moleculaire University of Rennes 1 U.R.A., C.N.R.S No. 1495 F-35042, Rennes, France 

Parthe (ed.), Modern Perspectives in Inorganic Crystal Chemistry, 17-26. 

At least two kinds of classes of transition metal compounds with metal - metal bonds can be distinguished  

The chemistry of the compounds of the early transition metals in low oxidation states is full of examples of the occurrence of metal - metal bonds. These compounds show unusual compositions in terms of the traditional valence rules metal - rich compounds contain more metal atoms than one expects for a normal valence compound (example Nbelii instead of Nbis). The transition metal elements on the left In the periodic system, and of those mainly the 4d and 5d elements, are capable of using the excess valence electrons, not needed to complete the octets of the anions, to fbnn metal -metal bonds. 

For metal - metal bonds between transition elements to occur, the major conditions are  

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There is a family of compounds known as Chevrel phases (Roger Chevrel, 1971) with the general formula MxMo6Xs, where M represents a rare earth metal, a transition or main group metal, and possibly a vacancy X can be S, Se, or Te. The idealized structure of PbMoftSs is... 

These are complex forms of M0S2 having the general formula M ,Mo6Xg, where M is a metal and X is a chal-cogen. PbMoeSs has the highest of the Chevral phases (Tc = 15 K). They are named after French scientist Roger Chevrel. 

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