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Metal Cluster Chemistry 409

are [Co 6 (CO) 16 ] and [Ir 6 (CO) 16 ]. Six metal clusters that early transition metal clusters have a nonmetal atom such
have a higher electron count adopt more open structures, as carbon or boron in the middle of the cluster; an example
such as the nearly flat arrangement for the metal atoms in is [(Zr 6 C)(Cl 15 )] , where a carbon atom resides inside a
−
2−
[Fe 3 Pt 3 (CO) 15 ] , which has a 90-valence electron count. Zr 6 octahedron and the Cl ligands surround the Zr 6 cluster.
Osmium, which is a cogener of iron, forms a significant The early transition metal cluster complexes often form
number of clusters containing ten Os atoms with a carbon extended arrays of cluster, which are joined by halide ions
2−
buried inside the cluster, such as [Os 10 C(CO) 24 ] . that bridge between the apexes of the component clusters.

III. EARLY TRANSITION METAL SEE ALSO THE FOLLOWING ARTICLES
CLUSTERS WITH HALIDE
AND ALKOXIDE LIGANDS
LIGANDFIELDCONCEPT•METALFORMING•METALHY-
DRIDES • METAL PARTICLES AND CLUSTER COMPOUNDS
To this point the descriptions of metal clusters has fo-
cused on transition metals ranging from the middle to the
right of the periodic table in low oxidation states. We now BIBLIOGRAPHY
turn to cluster compounds containing transition metals on
the left of the periodic table, which are often referred to
Braunstein, P., Oro, L. A., and Raithby, P. R. (1999). “Metal Clusters in
as early transition metals. In general, the early transition
Chemistry,” Vol. 2, Wiley—VCH, New York.
metal clusters have a strong affinity for halide and ox- Chisholm, M. H., ed. (1995). “Early Transition Metal Clusters with
ide ligands, referred to as hard ligands, which contrast π-Donor Ligands,” VCH, New York.
with the soft ligands such as CO and organic groups that Cotton, F. A., and Walton, R. A. (1993). “Multiple Bonds between Metal
dominate the metal cluster chemistry of the late transi- Atoms,” 2nd ed., Clarendon Press, Oxford.
Fackler, J. P., ed. (1990). “Metal–Metal Bonds and Clusters in Catalysis,”
tion metals described above. The metal atoms in the early
Plenum Press, New York.
transition metal clusters have positive oxidation states. As Shriver, D. F., Kaesz, H. D., and Adams, R. D., eds. (1990). “The Chem-
with some of the late transition metal clusters, some of the istry of Metal Cluster Complexes,” VCH, New York.