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Two novel open-cage fullerene derivatives bearing a 12-membered-ring orifice on the fullerene cage have been isolated. Removal of the N-MEM protective group leads to the first open-cage [60]fullerene derivative without organic addends on the rim of the orifice. [structure: see text]

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High-pressure resistivity experiments were performed on the recently discovered superconductor, MgB2. Tc decreases quasi-linearly with applied pressure to 1.4 GPa at a rate of -2.0(1) K GPa-1, which is somewhat larger than that derived from ac susceptibility measurements. The reduction of Tc is consistent with the BCS picture, in a similar way to the C60-based superconductors. Taking into account the pressure dependence of the unit cell volume, V, the volume coefficient of Tc, d(ln Tc)/dV is significantly large.

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Theoretical calculations have predicted all fullerene polymers to have interfullerene connections via ͓2 1 2͔ cycloaddition. We find that the ground state of Na 2 RbC 60 is a one-dimensional polymer of fullerene molecules connected by single carbon-carbon bonds. We discuss and exclude possible steric and kinetic reasons for this discrepancy. Our results imply that it is the charge state of the fullerene molecule that drives the bonding mechanism, causing ͑C 12 60 ͒ n and neutral ͑C 60 ͒ n to favor cycloaddition and ͑C 32 60 ͒ n to favor single carbon-carbon bonds. [S0031-9007(97)05104-1]