An EXAFS Study Of The Cluster Molecule Au55(PPh3)12Cl6

Gold L3 edge EXAFS has been used to study the coordination environment of gold atoms in the cluster molecule Au55(PPh3)12Cl6. The mean coordination of 7 by other gold atoms is consistent with a 3-shell cuboctahedral structure for the Au55 cluster. The first direct measurement of the Au-Au distance in this cluster shows that the spacing is significantly shorter than that in bulk metallic gold and is consistent with calorimetric work which has shown the Au-Au interactions are stronger in the cluster than in bulk gold. There is no evidence to suggest a significant spread of Au-Au distances in Au55(PPh3)12Cl6, in contrast to lower-nuclearity gold cluster molecules which have peripheral Au-Au distances typically 0.2Å longer than those to interstitial gold atoms.