Analogies between boron and carbon

Abstract

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 β-rhombohedral boron and fullerenes. The structural similarity of the pentagonal pyramidal C₆H₆²⁺ and MgB₄ is established. An interesting electronic structural relationship between the B₈₄ fragment of the β-rhombohedral boron and the fulleride anion, C₆₀^12-, is derived by replacing the 12 pentagonal pyramidal B₆^4- units by isoelectronic C₅^- units and removing the central B₁₂ from the electron-deficient B₈₄ unit. This relationship is well supported by the experimental realization of C₆₀M₁₂ (M = Li, K) and C₄₈N₁₂.