Large cluster complexes with almost 500 silver
atoms.
Nanoscopic �lumps� of atoms, known as clusters, are the specialty of a
research team headed by Dieter Fenske from the University of Karlsruhe
and the Forschungszentrum Karlsruhe. The production and characterization
of clusters made of interesting semiconductor materials are a main focus
of this group. As reported in the journal Angewandte Chemie, the team
has now been able to synthesize four new, particularly large and
silver-rich clusters, and to determine their crystal structures.
Two or three-dimensional nanostructures of semiconductor materials are
of interest for future nanoelectronic applications. Such structures
could be built of arrays of clusters. A cluster is an accumulation of
atoms or molecules that includes hundreds or thousands of atoms. Tiny
as they are, to some degree clusters have completely properties to
those of �normal sized� (macroscopic) solid particles. This difference
is caused by the high surface-to-volume ratio. In order to precisely
interpret the measured physical properties of clusters, it is
important to understand the atomic structure of these nanoparticles.
One of the things Fenske and his team are working on is the synthesis
of metal-rich clusters of the elements sulfur, selenium, and tellurium
(the chalcogens). For the metallic component in these systems, the
coinage metals copper and silver are well suited. By using specially
developed synthetic methods, the scientists were able to make
molecular cluster complexes. In this process, cluster cores made of
metal and chalcogen atoms are surrounded by a protective shell of
organic ligands. This protective coat prevents the tiny lumps from
aggregating into larger particles or solids. This trick made it
possible for the researchers to make particularly large silver-rich
clusters. The newest members of this family of clusters consist of
distorted spherical silver-chalcogenide cores with diameters between
two and four nanometers. Their surfaces are protected with thiolate or
phosphane ligands.
Characterizing the structures of such large metal-rich cluster
complexes by X-ray crystallographic studies is extremely difficult. It
is actually impossible to determine the exact composition. Defects in
the crystal lattice are one reason. The tendency to have defects
increases as the number of silver atoms grows. However, by using a
combination of X-ray diffraction, mass spectrometry, and electron
microscopy, the researchers did succeed in deriving idealized
empirical formulas and idealized atomic structures for their clusters.
The most silver-rich compound consists of clusters with approximately
490 silver and 188 sulfur atoms, as well as 114 sulfur-organic ligands,
and an idealized composition [Ag490S188(StC5H11)114].
Further Information
and Source:
-
Christopher E. Anson, Dr., Andreas Eichh�fer, Dr., Ibrahim Issac,
Dr., Dieter Fenske, Prof., Olaf Fuhr, Dr., Paloma Sevillano, Dr.,
Claudia Persau, Dr., Dietmar Stalke, Prof. Dr., Jiatao Zhang, Dr.: Synthesis and Crystal Structures of the Ligand-Stabilized Silver
Chalcogenide Clusters [Ag154Se77(dppxy)18],
[Ag320(StBu)60S130(dppp)12],
[Ag352S128(StC5H11)96],
and [Ag490S188(StC5H11)114].
In: Angewandte Chemie International Edition; published
Online: 4 Jan 2008;
doi 10.1002/anie.200704249.
