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Roald Hoffmann

Reasons to Be Interested in Carbides

As more carbon-rich carbides are synthesized, I think we will see other forms of C in them, and not only C, C2 and C3. In fact, I'm sure that little chunks of carbon will be made in solids in shapes that are so far unknown for carbon. Why? Well, every environment for the growth of an element (here carbon) creates its own "conditions of stability"—free in the gas phase or solution, on the surface of a metal, in the metal's interior, at an interface. This is how I think about the fact that buckminsterfullerene, C60, reached macroscopic stability—in the special reaction conditions of a carbon arc in a helium atmosphere. For most forms of carbon, survival after formation is guaranteed by the high barriers for breaking strong C-C bonds, even in strange, highly strained geometries. Based on what we know about the unusual geometrics of solid state borides (boron is next to carbon in the Periodic Table), it's just a matter of time until we find weird C-C bonding in carbides.

Finally, a personal view of the importance of the carbides. It's not in their economic value. Nor even in the simple to strange beauty of their structures, the paean to complexity they silently sing. No, their message is a spiritual one. The carbides are inorganic. Yet, ever so clearly, they are also organic—how else shall we think of those C-C bonds in many of them? Metal carbides are a bridge, the inherent link nature itself shows us, as we, in the simplicity of our minds, pigeonhole into one or another human-made category—organic, inorganic—the multifarious manifestations of one complex world.

© Roald Hoffmann

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