69,71Ga NMR studies of a superconducting Ga84 cluster compound

We present Ga-69,Ga-71-NMR experiments on microcrystalline samples of the recently discovered supramolecular compound Ga-84[N(SiMe3)(2)](20)Li6Br2(thf)(20).2toluene, which is composed of ligand-coordinated Ga-84 metal clusters, packed together in a fully ordered crystalline matrix. The compound is highly conducting and even shows superconductivity below T-c similar to 7.2 K. Our preliminary results between 10-300 K show a metallic-like behavior: the nuclear spin-lattice relaxation rate T-1(-1) follows the Korringa law (69)(T1T)(-1) = 0.36 s(-1)K(-1), but with a relaxation rate approximately three times smaller than in bulk alpha-Ga metal. No quantum-size effects are observed. the Korringa law being followed down to 10 K, whereas the quantum-gaps for individual clusters should amount to similar to 10(3) K. These results therefore suggest a transport process based on intermolecular charge transfer, similar as in alkali-doped fullerenes and silicon-clathrates.