Rhenium core composition

In the absence of experimental thermochemical evidence about the strength of the metal-carbon bonds in metal carbonyl carbide systems, we can turn to the binary compounds formed between transition metals and carbon for information about the last point, the strength of metal-carbon bonds to core carbon atoms. Transition metal carbides are important. They include, in substances such as tungsten carbide, WC, some of the hardest substances known, and the capacity of added carbon to toughen metals has been known since the earliest days of steel-making. Information about them is, however, patchy. They are difficult to prepare in stoichiometric compositions of established structure and thermochemistry the metals we are most interested in here (osmium, rhenium, and rhodium) are not known to form thermodynamically stable binary phases MC and the carbides of some other metals adopt very complicated structures. Enough is, however, known about the simple structures of the carbides of the early transition metals to provide some useful pointers. 

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