INTERCALATION OF SOLID C-60 WITH IODINE

METALLIC and superconducting donor-type intercalation compounds of C60 are now well established. These involve electron transfer from a sublattice of alkali-metal dopants to a sublattice of fullerene molecules. Three stoichiometric phases have been identified 1-3, and a binary phase diagram describing composition regions of two-phase coexistence has been proposed 2. Oxidative intercalation by electron acceptors, meanwhile, has not previously been reported. Ohno et al. 4 recently presented photoemission data suggesting that solid C60 Will take up only minor amounts of iodine, resulting in a non-metallic product which is not a stoichiometric compound 4. Here we report that, by using different reaction conditions, we have prepared a highly crystalline C60: iodine compound of ideal stoichiometry C60I4, with an alternating guest-host layer structure closely resembling that of classic intercalation compounds. The 300-K resistivity exceeds 10(9) OMEGA-cm and we observe no superconductivity down to 4 K, despite the fact that the inter-fullerene separation lies in the range of that in the superconducting M3 C60 phases (where M is K, Rb, Cs). C60I4 is apparently the first example of a fullerite intercalation compound in which there is no electron transfer between C60 and the intercalate.