Clusters on clusters. Closo-dodecaborate as a ligand for Au55 clusters.
The exchange of PPh3 in Au55(PPh3)12Cl6 by Na2[B12H11SH] using a phase-transfer reaction from CH2Cl2 to water needs 6 wk for reaction, but finally results in the quant. formation of Au55[(B12H11SH)Na2]12Cl6 (I). Cluster I, which is of considerable stability in aq. soln., was characterized by 1H-NMR, 11B-NMR, and IR spectroscopy as well as by TEM. The Na+ cations can be exchanged by (octyl)4N+ making the resulting cluster (II) sol. in polar org. solvents. The elec. properties of I and II are compared with those of Au55[Ph2PC6H4SO3N(octyl)4]12Cl6 (III), the NH4 deriv. of the Na salt. Cluster III shows the expected increase of activation energy in the temp. range of 130-250 K owing to the increase of cluster spacing compared with the Na deriv. However, clusters I and II, show electromigration in the elec. field, caused by the huge amt. of ionic charges in the ligand shell.
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