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Systematic studies of large, ligated transition-metal clusters possessing direct metal-metal connectivities are carried out by only a few research groups throughout the world. Perhaps none surpasses the scope—and the longevity—of Lawrence F. Dahl and his group at the University of Wisconsin, Madison. Dahl has spent much of the past 50 years exploring clusters that have at least 10 and usually up to about 50 metal atoms.
But during the past decade, Dahl and coworkers have greatly exceeded those numbers to achieve crystallographically determined records for clusters of this type, with the formulas Pd145(CO)x(P[CH2CH3]3)30, where x ~ 60, and Pd165- xPtx(CO)72(P[C6H5]3)20, where x ~ 8. These superclusters are arrayed in multiple concentric spherical shells, and each has the same third-shell polyhedron of 60 metal atoms, which is a stereoisomer of the C60 buckyball.
“Synthesis and structural characterization of large metal clusters by Dahl and coworkers will rank high on any list of the most challenging and significant accomplishments in inorganic synthesis in recent years,” his Wisconsin colleague Paul M. Treichel comments.
In the early years, Dahl’s group carried out syntheses and crystallographic characterizations of relatively small clusters whose metal-core architectures were primarily governed by changes in valence electronic configuration. The systematic analyses of the observed geometrical variations that occurred upon addition or loss of valence electrons provided significant insight concerning the electronic metal-core configurations—that is, experimental quantum mechanics—and emphasized the stereochemical importance of electrons occupying antibonding metal-cluster orbitals for small clusters.
Later on, his group’s activities focused on nanosized metal-carbonyl clusters containing group 10 (Ni, Pd, Pt) and combined group 10/group 11 (Cu, Ag, Au) elements. These nanoclusters, including the record-setting giants, are possible precursors of new materials with useful catalytic, electronic, magnetic, and optical properties, Dahl notes. Because structural analyses have given rise to proposed sequential growth pathways, the clusters can be compared with larger noncrystalline naked/ligated nanoparticles and consequently should attract attention among scientists in nanoscience and nanotechnology, he adds.
Dahl, 80, received a B.S. in 1951 from the University of Louisville and a Ph.D. in 1957 from Iowa State University, where his adviser was the late Robert E. Rundle. He began his teaching and research career at Wisconsin in 1957, and he currently is the R. E. Rundle Professor of Chemistry and a Hilldale Professor.
Among his honors, awards, and lectureships, Dahl received Alfred P. Sloan (1963) and Guggenheim (1969) fellowships, a Chemical Pioneer Award from the American Institute of Chemists (2000), the Nyholm Medal from the Royal Society of Chemistry (1985), an Alexander von Humboldt Senior Scientist Award (1985), the ACS Award in Inorganic Chemistry (1974), and the Willard Gibbs Medal from the ACS Chicago Section (1999). He is a member of the National Academy of Sciences and the American Academy of Arts & Sciences.
Although Dahl formally retired in 2008 after mentoring 95 Ph.D. students, he continued to voluntarily teach general chemistry and crystallography and is still engaged in research. This past September, Dahl presented a short course on chemical crystallography to undergraduate students and faculty at Grinnell College. Dahl also has achieved fame for his exorbitant use of slides in research talks—the “Dahl unit” denotes one filled slide-carousel tray containing 80 slides.
Dahl will present the award address before the Division of Inorganic Chemistry.
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