Henry Rzepa's Blog

C₂ (dicarbon) is certainly interesting from a theoretical point of view. Whether or not it can be described as having a quadruple bond has induced much passionate discussion[cite]10.1038/nchem.1263[/cite],[cite]10.1002/anie.201208206[/cite],[cite]10.1002/anie.201301485[/cite],[cite]10.1002/anie.201302350[/cite]. Its occurrence in space and in flames is also well-known. But does it have what might be called a conventional chemistry? Other highly reactive species (cyclobutadiene is a well-known example) can often be tamed by trapping as a ligand coordinated to a metal and so one might speculate upon how C₂ responds to the proximity of a metal. As is noted here[cite]10.1002/anie.201208206[/cite], dicarbon as a ligand has been known a long time as part of what is referred to as carbide chemistry. In this regard it is thought of as the di-anion, C₂^2- (and isoelectronic therefore with dinitrogen). Thus calcium carbide, but in fact the degree to which the dicarbon can absorb electrons is thought to be wide (as judged by the resulting C-C bond length, see[cite]10.1002/anie.201208206[/cite]). Here I take a look at just one metal carbide[cite]10.1016/j.jssc.2008.08.005[/cite] that caught my eye (there are hundreds of others, many no doubt equally interesting!).

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