Naked Au55 clusters: dramatic effect of a thiol-terminated dendrimer.
Reaction of the thiol-terminated 4th-generation dendrimer 2-G4 (96 SH groups) with the Au cluster compd. Au55(PPh3)12Cl6 in a 3:1 molar ratio in CH2Cl2 gave bare Au55 clusters. The cuboctahedrally shaped Au55 particles coalesce to well-formed microcrystals (Au55).... The role of the dendrimer is not only to remove the phosphine and Cl ligands but also to act as an ideal matrix for perfect crystal growth. TEM, small- and wide-angle x-ray diffraction (SAXRD and WAXRD) measurements indicate a structure where rows of edge-linked Au55 building blocks form a distorted cubic lattice. The x-ray data fit best if a 5% redn. of the Au-Au bond length in the Au55 clusters is assumed, in agreement with previous extended x-ray absorption fine structure (EXAFS) measurements. Energy-dispersive x-ray spectroscopy (EDX) analyses and IR studies show the absence of PPh3 and Cl in the microcrystals.
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