Bigger with Platinum

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Science  21 Sep 2007:
Vol. 317, Issue 5845, pp. 1651
DOI: 10.1126/science.317.5845.1651c

Palladium is exceptional in its tendency to form large well-defined clusters capped with CO and phosphine ligands; clusters with up to 145 Pd atoms have been characterized. Mednikov et al. now report that platinum can get into the act if the synthesis starts with a smaller Pd cluster, Pd10(CO)12(PPh3)6 (where PPh3 is triphenylphosphine), which reacts with added Pt(CO)2(PPh3)2 to yield a 165-atom Pt-Pd cluster, nominally Pd157Pt8(CO)72(PPh3)20. The crystallographic occupancy analysis was augmented by wide-angle dispersive spectroscopy to establish the Pt stoichiometry. The structure can be described as four concentric shells. At the center is a Pt atom, surrounded by a 12-atom Pd icosahedron, and the second shell is a 42-atom icosahedron with either 3 or 4 Pt atoms; the third and fourth shells are high-symmetry structures with 60 and 50 atoms, respectively. This cluster is unusual in that its outermost shell has fewer atoms than the underlying shell, and CO ligands bridge intershell metal atoms. — PDS

J. Am. Chem. Soc. 129, 10.1021/ja073945q (2007).

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