Two Ih-symmetry-breaking C60 isomers stabilized by chlorination

One abiding surprise in fullerene science is that I(h)-symmetric buckminsterfullerene C(60) (ref. 1) (I(h)-C(60) or (#1,812)C(60), the nomenclature specified by symmetry or by Fowler's spiral algorithm(2)) remains the sole C(60) species experimentally available. Setting it apart from the other 1,811 topological isomers (isobuckminsterfullerenes) is its exclusive conformity with the isolated-pentagon rule(3), which states that stable fullerenes have isolated pentagons. Although gas-phase existence of isobuckminsterfullerenes has long been suspected(4-7), synthetic efforts have yet to yield successful results. Here, we report the realization of two isobuckminsterfullerenes by means of chlorination of the respective C(2v)-and C(s)-symmetric C(60) cages. These chlorinated species, (#1,809)C(60)Cl(8)(1) and (#1,804)C(60)Cl(12)(2), were isolated in experimentally useful yields. Structural characterization by crystallography unambiguously established the unique pentagon-pentagon ring fusions. These distinct structural features are directly responsible for the regioselectivity observed in subsequent substitution of chlorines, and also render these unprecedented derivatives of C60 isomers important for resolving the long-standing puzzle of fullerene formation by the Stone-Wales transformation scheme(8-11).