Clusters on clusters: closo-dodecaborate as a ligand for Au-55 clusters

The exchange of PPh3 in Au-55(PPh3)(12)Cl-6 by Na-2[B12H11SH] using a phase -transfer reaction from CH2Cl2 to water needs 6 weeks for reaction, but fin ally results in the quantitative formation of Au-55[(B12H11SH)Na-2] Cl-12(6 ) (2) Cluster 2, which is of considerable stability in aqueous solution, ha s been characterized by H-1-NMR, B-11-NMR, and IR spectroscopy as well as b y transmission electron microscopy (TEM). The Na+ cations can be exchanged by (octyl)(4)N+ making the resulting cluster 4 soluble in polar organic sol vents. The electrical properties of 2 and 4 are compared with those of Au-5 5[Ph2PC6H4SO3N(octyl)(4)](12)Cl-6 (3), the ammonium derivative of the sodiu m salt. Cluster 3 shows the expected increase of activation energy in the t emperature range of 130-250 K owing to the increase of cluster spacing comp ared with the;odium derivative. However, clusters 2 and 4, show electromigr ation in the electric field, caused by the huge amount of ionic charges in the ligand shell.