Carbides

Roald Hoffmann

Trapped in the Solid State

Consider still another Jeitschko structure, made of yttrium, cobalt and carbon—YCoC (Figure 5). Through it run infinite [CoC]^3– needles, with a cobalt-carbon separation that is tied (with a discrete molecule) for the world's record for shortest Co-C distance (1.85 angstroms). The Co-C separation in the naturally occurring molecule vitamin B₁₂ is substantially longer.

Figure 5. A piece of the yttrium cobalt carbide . . .

In YCoC there is a CoC^3–organometallic polymer, multiply bonded between Co and C, judging from that short distance. The polymer is trapped in the solid state. A theoretical chemist wishing to provoke his uppity experimental colleagues (that's me) says, "Get it out of there, solubilize that polymer, give it—in a solvent—a better Lewis acid partner than Y³⁺." Of course, they won't get it out. But this structure should be an inspiration to molecular organometallic chemists making rodlike polymers; they're possible, waiting to be made outside the solid.

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