Physics and Chemistry of Metal Cluster Compounds: Model Systems for Small Metal Particles

325 Pages·1994·9.294 MB·English

by  L. J. De Jongh (auth.), L. J. De Jongh (eds.)

PHYSICS AND CHEMISTRY OF METAL CLUSTER COMPOUNDS
Physics and Chemistry of Materials
with Low-Dimensional Structures
VOLUME 18
Editor-in-Chief
F. LEVY, Institut de Physique Appliquee, EPFL,
Departement de Physique, PHB-Ecublens, CH-I015 Lausanne, Switzerland
Honorary Editor
E. MOOSER, EPFL, Lausanne, Switzerland
International Advisory Board
J. V. ACRIVOS, San Jose State University, San Jose, Calif., U.S.A.
S. BARISIC, University of Zagreb, Department of Physics, Zagreb, Croatia
J. G. BEDNORZ, IBM Forschungslaboratorium, Ruschlikon, Switzerland
C. F. van BRUGGEN, University of Groningen, Groningen, The Netherlands
R. GIRLANDA, Universita di Messina, Messina, Italy
D. HAARER, University of Bayreuth, Germany
A. J. HEEGER, University of California, Santa Barbara, Calif., U.S.A.
H. KAMIMURA, Dept. of Physics, University of Tokyo, Japan
W. Y. LIANG, Cavendish Laboratory, Cambridge, U.K
P. MONCEAU, CNRS, Grenoble, France
J. ROUXEL, CNRS, Nantes, France
M. SCHLUTER, AT&T, Murray Hill, N.J., U.S.A.
I. ZSCHOKKE, Universitiit Basel, Basel, Switzerland
The titles published in this series are listed at the end of this volume.
PHYSICS AND CHEMISTRY
OF
METAL CLUSTER COMPOUNDS
MODEL SYSTEMS FOR SMALL METAL PARTICLES
Edited by
L. J. DE JONGH
Kamerlingh Onnes Laboratory,
Leiden University,
The Netherlands
KLUWER ACADEMIC PUBLISHERS
DORDRECHT/BOSTON/LONDON
Library of Congress Cataloging-in-Publication Data
Physics and chemistry of metal cluster compounds model systems for
small metal particles / edited by L.J. de Jongh.
p. cm. -- (Physics and chemistry of materials with low
-dimensional structures; v. 18)
Includes index.
ISBN 978-90-481-4369-6 (ac i d free paper)
1. Metal crystals. 2. Metal-metal bonds. I. Jongh. L. J. de.
II. Series.
OD921.P48 1994
546.3--dc20 93-49928
ISBN 978-90-481-4369-6 ISBN 978-94-015-1294-7 (eBook)
DOI 10.1007/978-94-015-1294-7
Published by Kluwer Academic Publishers,
P.O. Box 17,3300 AA Dordrecht, The Netherlands.
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© 1994 Kluwer Academic Publishers
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TABLE OF CONTENTS
PREFACE IX
1. L. J. DE JONGH / Introduction to Metal Cluster Compounds:
From Molecule to Metal! 1
1.1. The impact of cluster-science 1
1.2. Structural characteristics of metal clusters 4
1.3. Electronic energy-level structures 10
1.4. Brief introduction to the physical properties of
metal cluster compounds 19
1.5. Conductivity studies 25
1.6. Application of the Anderson-Hubbard approach 31
References 37
2. A. CERIOTTI, R. DELLA PERGOLA AND L. GARLASCHELLI /
High-Nuclearity Carbonyl Metal Clusters 41
2.1. Introduction 41
2.2. Synthesis and reactivity 49
2.3. Structural aspects 67
2.4. Electron counting for clusters 93
References 101
3. G. SCHMID / Ligand-Stabilized Giant Metal Clusters and Colloids 107
3.1. Strategy for making giant metal clusters 107
3.2. Synthetic and structural examples 109
3.2.1. Ligand-stabilized colloids 109
3.2.2. Ligand-stablized clusters 116
3.3. Chemical properties 122
3.4. Catalysis 127
3.5. Outlook 131
References 133
4. D. E. ELLIS / Theory of Electronic Properties of Metal
Clusters and Particles 135
4.1. Why are metal particles interesting? 135
4.2. Model Hamiltonians 136
VI TABLE OF CONTENTS
4.3. Traditional quantum chemical methods 141
4.4. Density functional approaches 144
4.4.1. Alkali metal clusters 145
4.4.2. Cluster compounds 146
4.4.3. Transition metal particles: free and embedded 148
4.5. Summary 153
References 155
5. R. ZANONI/X-Ray Photoelectron Spectroscopy Applied to
Pure and Supported Molecular Clusters 159
5.1. Introduction 159
5.2. Generalities of photoemission spectroscopy applied to pure
and supported molecular metal clusters 160
5.3. XPS of molecular clusters 169
5.4. XPS of supported molecular clusters 175
5.5. Outlook for the future 179
References 180
6. R. C. THIEL, H. H. SMIT AND L. J. DE JONGH / Application of
Mossbauer Effect Spectroscopy to Cluster Research 183
6.1. Introduction 183
6.2. Mossbauer Effect Spectroscopy (MES) 183
6.2.1. Elements of MES 183
6.2.2. MES specific to clusters 188
6.2.3. Previous MES measurements on gold particles 189
6.3. Our Mossbauer results 191
6.3.1. Thermal behaviour 191
6.3.2. Electronic behaviour 196
6.3.3. Effect ofligand modification 198
6.4. 197 Au MES on platinum clusters 201
6.5. Conclusions 206
References 207
7. H. B. BROM, J. BAAK AND L. J. DE JONGH / Specific Heat
Studies on Metal Cluster Compounds 211
7.1. Introduction 211
7.2. The lattice specific heat 212
7.2.1. The elastic continuum approximation 212
7.2.2. The molecular dynamics approach 215
7.2.3. A spherical309-atomic Pt-particle as example 216
7.3. The electronic specific heat 217
7.3.1. The degenerate electron gas. Surface effects and bulk states 218
7.3.2. The Quantum-Size limit 219
TABLE OF CONTENTS vii
7.4. Data and discussion 220
7.4.1. Small metal particles 220
7.4.2. Metal cluster compounds 221
7.5. Summary 225
References 225
8. H. B. BROM, D. VAN DER PUTTEN AND L. J. DE JONGH /
NMR in Submicron Particles 227
8.1. Introduction 227
8.2. Surface and quantum size effects 228
8.2.1. Surface effects 229
8.2.2. Quantum size effects 229
8.3. ESR and NMR - Theory 230
8.3.1. ESR 231
8.3.2. NMR 232
8.4. Naked clusters - Experiment and discussion 234
8.4.1. ESR 235
8.4.2. NMR 235
8.5. Aggregates of metal cluster compounds-
Experiment and discussion 237
8.5.1. Core-resonance 237
8.5.2. Ligand-shell resonance 242
8.5.3. Results from other experiments 245
8.6. Summary 246
References 246
9. R. E. BENFIELD / Magnetic Properties and UV-Visible
Spectroscopic Studies of Metal Cluster Compounds 249
9.1. Introduction 249
9.2. Magnetic properties 250
9.2.1. Magnetic susceptibility of low-nuclearity clusters 250
9.2.2. Magnetic susceptibility of high-nuclearity clusters 253
9.2.3. EPR studies of decanuclear osmium clusters 256
9.2.4. EPR studies of rhodium carbonyl clusters 262
9.2.5. EPR studies of other high-nuclearity clusters 263
9.3. Electronic (UV-visible-NMR) spectra 264
9.3.1. One-electron absorptions 264
9.3.2. Interband transitions 265
9.3.3. Plasma resonance absorptions 268
9.3.4. Charge transfer in the solid state 270
9.4. Conclusion 272
viii TABLE OF CONTENTS
Acknowledgements 272
References 272
10. J. M. VAN RUITENBEEK, D. A. VAN LEEUWEN AND
L. J. DE JONGH / Magnetic Properties of Metal Cluster Compounds 277
10.1. Introduction 277
10.2. Magnetic properties of atoms, metals and clusters 278
10.2.1. Atoms 280
10.2.2. Metals 282
10.2.3. Clusters 285
10.2.3.1. The spin susceptibility in metal clusters 286
10.2.3.2. The orbital susceptibility in metal clusters 289
10.2.3.3. Exchange and correlation effects 295
10.2.3.4. The spin-orbit interaction 295
10.2.3.5. Ligand coordination: Suppression and magnetisim 296
10.3. Experiments on metal cluster compounds 297
10.3.1. The spin susceptibility 297
10.3.1.1. The even-odd dichotomy 297
10.3.1.2. Pauli paramagnetism 298
10.3.1.3. Clusters containingNi or Co 301
10.3.2. The orbital magnetic susceptibility 304
References 305
INDEX OF CHEMICAL COMPOUNDS 307
INDEX OF SUBJECTS 315
PREFACE
On Friday, February 20, 1980, I had the pleasure to be present at the inaugural
lecture of my colleague Jan Reedijk, who had just been named at the Chair
of Inorganic Chemistry of Leiden University. According to tradition, the
ceremony took place in the impressive Hall of the old University Academy
Building. In the course of his lecture, Jan mentioned a number of recent
developments in chemistry which had struck him as particularly important or
interesting. Among those was the synthesis of large metal cluster compounds,
and, to my luck, he showed a slide ofthe molecular structure of [PtI9(C)b]4-.
(To my luck, since at traditional Leiden University it is quite unusual to show
slides at such ceremonies.) This constituted my first acquaintance with this
exciting new class of materials. I became immediately fascinated by this
molecule, partly because of the esthetic beauty of its fivefold symmetry,
partly because as a physicist it struck me that it could be visualized as an
"embryonically small" metal particle, embedded in a shell of CO ligands.
It came to me as a surprise that Nature could provide us with such a
"chemical nanostructure", with its combination of metal-metal and metal
ligand bonds. However, when I later asked Jan about it, he mentioned that,
to all probability the metal-ligand interactions should have washed out all
potential metallic properties of the metal cluster core. Although I retorted
that, still, there were two Pt atoms situated in the interior ofthe Pt19 core, and
thus totally surrounded by the 17 other Pt atoms, we left the matter there at
the time.
But the thought never left my mind so I brought it up from time to time
and about three years later Jan passed me a copy of the memorable review
paper by Muetterties entitled "Metal Clusters: Bridges between molecular
and solid-state chemistry" (C & EN, Aug. 30, 1982, p. 28). From this paper
I learnt that, next to the [PtI9(CO)22]4- cluster, many polynuclear metal
cluster compounds had been synthesized already, some with metal cores
even considerably larger, as in e.g. [Pt38(CO)44Hx]2-, also synthesized by
the group in Milano. I became definitively convinced that there should be a
promising future in these materials as model systems for small metal particles
embedded in a dielectric solid.
Since my colleagues Hans Brom and Roger Thiel in our Solid State Physics
group also became enthusiastic for the idea, it was decided to try to contact
a number of the chemist groups involved in the synthesis of these materials.
Via Jan Reedijk, I was introduced to Jan Steggerda (Nijmegen University),
and later to Gunter Schmid (Universitat Essen) who had just synthesized
L.l. de longh (ed.), Physics and Chemistry of Metal Cluster Compounds, ix-xi.
© 1994 Kluwer Academic Publishers.
x PREFACE
his, by now well-known, 55 metal atom clusters. Subsequently, contacts
were made with Giuliano Longoni and Alessandro Ceriotti in Milano, and
with Brian Johnson and Robert Benfield in England. It turned out that, at
that time, the synthetic chemists involved with clusters had reached a stage
where they really welcomed the arrival of a couple of physicists eager to
start to study in detail the physical properties of their materials. So, a happy
collaboration evolved, which, in the course of time, has proven to be very
fruitful. It should be mentioned that from the very beginning the project
has received the well-appreciated support from the European Community
research stimulation programs, first under the Laboratory Twinning Program,
then under the Science Program. More recently, Roberto Zanoni (Roma),
Herman van Kempen (Nijmegen), Gianfranco Pacchioni (Milano) and Notker
Rosch (Miinchen), have also joined our ranks.
The aim of this book is to present a first review of what we have learnt in the
last eight years about the physical properties of these fascinating compounds.
Since almost nothing was known in the beginning, we had to start from
scratch, and only gradually, with ups and downs, our understanding has
begun to develop. Evidently, the most important and challenging problem to
unravel was the evolution with cluster size from "molecular" to "metallic"
behavior. The advent of the giant clusters, containing as much as 309 Pt
atoms or 561 Pd atoms (made by Giinter Schmid), has greatly facilitated our
task. Together with the availability of colloids of the same metal with narrow
size distributions, the original dream we had at the start is now realised to
a great extent: to be able to study the physical properties of metal particles
of well-defined, homogeneous size as a function of increasing size. Thus the
time seemed ripe to collect our present understanding of the problem in the
form of a book, also with the idea to interest more physicist colleagues in
these still relatively unknown materials.
As will be seen from this book, the transition from molecular to metallic
behavior is probably a gradual one, with a substantial transition region in
between where properties are neither molecular nor metallic. I have earlier
proposed the names "meta-metallic" and/or "proto-metallic" for the behavior
in this intermediate regime. In view of the latest developments in nomen
clature, we might as well adopt the term "mesoscopic metallic", or "meso
metallic" in short. What is important is that the onset and end of this region
is certainly not universal. Even for one and the same metal it depends on the
physical property one is studying and even on the temperature at which the
experiment is performed.
Let me end by thanking whole-heartedly the numerous colleagues who
have made invaluable contributions to this book, either directly or indirectly.
I am particularly grateful, of course, to all the authors and coauthors of the
various chapters. Knowing how busy lives these colleagues lead makes me
all the more thankful for their willingness to spend their precious time on
the realisation of this venture. I can only express my hope that they will