CHEMISTRY: Pd145 Reveals Its Secrets

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Science  17 Nov 2000:
Vol. 290, Issue 5495, pp. 1261b
DOI: 10.1126/science.290.5495.1261b

Small clusters of atoms containing a few hundred atoms may form structures that differ from those of their bulk counterparts. A well-known example is the formation of icosahedral clusters; this structure cannot be extended in all directions (a prerequisite for the formation of regular crystals) because of strain, but at small sizes it may be energetically advantageous.

Tran et al. have prepared high-quality crystals of highly symmetric clusters, each containing 145 palladium atoms. Their high-resolution crystal structure shows that the inner two layers of each cluster (blue, red), formed by 55 atoms, are icosahedral. The third layer (green), formed by 60 atoms, has a regular and more complex symmetry unlike that of C60, and represents a complete layer in one of two proposed cluster growth routes for the 55-atom icosahedron. The remaining 30 palladium atoms (orange) cap the square faces in the third layer and bind a triethylphosphine ligand (purple). About 60 disordered carbon monoxide molecules surround the cluster. The level of structural detail obtained by the authors is unprecedented for a large metal cluster and provides insights into the forces stabilizing metal clusters. — JU

Agnew. Chem. Int. Ed. 39, 4121 (2000).

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