Synthesis and Single-Crystal X-ray Structure of a Highly Symmetrical C ₆₀ Derivative, C ₆₀ Br ₂₄

Abstract

C(60) and liquid bromine react to form C(60)Br(24), a crystalline compound isolated as a bromine solvate, C(60)Br(24)(Br(2))(x), The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C(60) framework is recognizable in C(60)Br(24), but sp(3) carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150 degrees to 200 degrees C there is effectively quantitative reversion of C(60)Br(24) to C(60) and Br(2).

X-ray Powder Diffraction Structure of Triclinic C60Br24(Br2)2

“…C60 was dissolved in a large excess of bromine and the red solution stirred at 300 K for 8 d in the dark under argon. Excess bromine was removed by the bubbling of Table 1), with structure of Tebbe et al (1992).…”

“…C60Br24(Bre)2 was prepared using a slight modification of the procedure of Tebbe et al (1992). (We discuss the assignment of the amount of interstitial Br2 below.)…”

“…The lattice constants after refinement with LSUCRE (Evans, Appleman & Handworker, 1963) are a = 14.309, b = 17.182, c = 12.964A, ~ -96.798, fl = 93.362 and ~, = 89.990 °. From the known diameter (,~ 13 ~) of the C60Br24 molecule (Tebbe et al, 1992), it appears that this is a pseudocentered cell. Indeed, we found that the reduced cell indexed the pattern equally well (a = 14.309, b = 12.570, c = 12.964/~, ~ = 62.557, fl = 93.362 and ~ = 57.382°).…”

“…Recent developments are reviewed by, for example, Taylor & Walton (1993). The molecule C60Br24 was synthesized by Tebbe et al (1992), who determined the structure of the molecule from single-crystal X-ray data. The modified fullerene molecule ( Fig.…”

“…1), which has m3 (Th) symmetry, is saturated with bromine, in the sense that 24 is the maximum number of Br-atom additions that can be made without two Br atoms being bonded to adjacent C atoms. Tebbe et al (1992) studied single crystals grown by slow precipitation from a solution of C60 and liquid bromine at elevated temperature. Their crystals, which displayed a rhombohedral lattice slightly distorted from face-centered cubic, had nominal stoichiometry C60Br,,, with n = 25-28; those bromines not covalently bonded to the C60 shell were distributed in the lattice as interstitial Br2.…”