Page 294 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

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Encyclopedia of Physical Science and Technology EN010H-470 July 16, 2001 16:53

Nanosized Inorganic Clusters

Leroy Cronin Dieter Fenske
Achim M¨uller University of Karlsruhe, Germany
University of Bielefeld, Germany

I. From Clusters to the Boundary
of the Metallic State
II. From Clusters to Segments of Solid-State
Structures
III. From Building Blocks Via Clusters to Solids
IV. Conclusions and Perspectives

GLOSSARY relevance in this article are those clusters that are suffi-
ciently well-defined and large enough to be at the bor-
Cluster Group of atoms bound together. derline between the molecule and the bulk. It is in this
Colloid Particle small enough to remain suspended in area that materials with extremely interesting properties
solution or gas. have begun to have a profound influence on basic science
Icosahedron A polyhedron having 20 faces and 12 as well as technology from catalysis to electronically in-
vertices. teresting materials. Such materials become even more in-
Ligand Molecule bound to a metal atom or cluster. teresting when they are themselves, as building blocks,
Nucleation The condensation or aggregation process by organized into a bulk material in a predesigned, desired
which crystals are formed on a minute amount of sub- manner. It is the fabrication of inorganic nanoclusters that
stance that acts as a nucleus for subsequent crystalline lies at the cutting edge of nanodesign and technology to-
growth. day and promises many exciting discoveries and applica-
tions tomorrow. We refer here to three important classes
of molecular clusters which have been thoroughly charac-
NANOSIZED CLUSTERS or “nanoclusters” is a term terized and can be seen to be entering the size regime of
given to particles of any kind of matter, the size of which is mesoscopic materials.
greater than that of typical molecules, but is too small to
exhibit characteristic bulk properties. Examples of such
materials include the family of carbon-based fullerenes, I. FROM CLUSTERS TO THE BOUNDARY
weakly bound van der Waals clusters observed in the gas OF THE METALLIC STATE
phase, metal carbonyl clusters, boron carbides and hy-
drides, metal clusters surrounded by protecting ligands, Giant metal-based clusters serve as a bridge between
and metal ions connected by bridging ligands. Of special molecular clusters and bulk metals. This has implications

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