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Encyclopedia of Physical Science and Technology EN009I-110 July 18, 2001 0:40

Metal Cluster Chemistry

D. F. Shriver
Northwestern University

I. Introduction
II. Representative Transition Metal Cluster
Compounds
III. Early Transition Metal Clusters with Halide
and Alkoxide Ligands

GLOSSARY A METAL CLUSTER compound usually consists of a
polyhedral array of metal atoms that are held together by
Butterfly geometry An array of atoms consisting of two metal–metal bonds. This metal cluster is surrounded by
triangles that share a common edge, where the metal ligands that may be small molecules or ions, such as CO or
atoms are located at the vertices of the triangles. Cl . An important tool in the development of metal clus-
−
Electron count The number of valence electrons on an ter chemistry is single-crystal X-ray diffraction, which is
atom or molecule. used to determine the arrangement of the atoms in metal
Halides The elements in column 17 of the periodic table: clusters. The structures illustrated in this section were de-
F, Cl, Br, I, and At. termined by X-ray diffraction. It is important to note that
Ligand An anion or neutral molecule that bonds to a the formation of cluster compounds is not limited to the
metal atom by donating a pair of electrons to the metal elements. Nonmetal clusters are also known such as
metal. P 4 and C 60 .
Maingroupmetals Theelementsinthefirsttwocolumns
of the periodic table, excluding hydrogen.
Metal–metal bond A bond between two metal atoms in I. INTRODUCTION
a metal cluster compound.
Transition metals The elements located in columns 3–10 Many of the early discoveries of metal cluster compounds
in the periodic table. occurred in the research laboratory of Professor Walter
Valence electrons The outermost electrons on an atom, Hieber at the University of Munich in the early 1900s.
which may form bonds with valence electrons on ad- Hieber’s cluster compounds consisted of transition metals
jacent atoms. that have metal–metal bonds, and carbon monoxide lig-
X-ray diffraction The reflection of an X-ray beam by a ands are attached to the metal cluster. However, Hieber
solid, which may be analyzed to determine molecular knew only the composition of his newly discovered com-
structure. pounds. Eventually their structures were determined by

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