Analogies between boron and carbon

The structural connections between the compounds of boron and carbon are extended using the mno rule beyond the borane-carbocation continuum, the lithium boride-polycarbyne analogy, and the magnesium boride (MgB2)-graphite equivalence to beta-rhombohedral boron and fullerenes. The structural similarity of the pentagonal pyramidal C6H62+ and MgB4 is established. An interesting electronic structural relationship between the B-84 fragment of the beta-rhombohedral boron and the fulleride anion, C-60(12-), is derived by replacing the 12 pentagonal pyramidal B-6(4-) units by isoelectronic C-5(-) units and removing the central B-12 from the electron-deficient B-84 unit. This relationship is well supported by the experimental realization of C60M12 (M = Li, K) and C48N12.