Endofullerenes: A New Family of Carbon Clusters

297 Pages·2002·8.61 MB·English

by  Martin Saunders

Endofullerenes
Developments in Fullerene Science
Volume 3
Series Editor:
Tibor Braun, Institute of Inorganic and AnaZyticaZ Chernistry, L. Eötvös University, Budapest,
Hungary
The titZes pubZished in this series are listed at the end of this voZurne.
Endofullerenes
A New Family of Carbon Clusters
Edited by
Takeshi Akasaka
TARA Center,
University ofTsukuba,
Tsukuba, Japan
and
Shigeru Nagase
Institute for Molecular Science,
Okazaki, Japan
SPRINGER-SCIENCE+BUSINESS MEDIA. B.Y.
A C.I.P. Catalogue record for this book is available from the Library of Congress.
ISBN 978-90-481-6159-1 ISBN 978-94-015-9938-2 (eBook)
DOI 10.1007/978-94-015-9938-2
Printed on acid-free paper
All Rights Reserved
© 2002 Springer Science+Business Media Dordrecht
Originally published by Kluwer Academic Publishers in 2002
Softcover reprint of the hardcover 1st edition 2002
No part of this work may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, rnicrofilming, recording
or otherwise, without written perrnission from the Publisher, with the exception
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and executed on a computer system, for exclusive use by the purchaser of the work.
TABLE OF CONTENTS
Foreword vii
1. Putting nonmetals into fullerenes 1
M. Saunders and J. Cross (Yale University)
2. Group V endohedral fullerenes: N@C60, N@C70, and P@C60 13
B. Pietzak (SONY Corporation), A. Weidinger (Hahn-Meitner-
Institute), K.-P. Dinse (Technical University of Darmstadt), A. Hirsch
(University of Erlangen)
3. Collisional production and characterization of alkali endohedral
fullerenes 67
E. E. B. Campbell (Gothenburg University and Chalmers University
of Technology)
4. Structures and electronic properties of endohedral metallofullerenes;
theory and experiment 99
K. Kobayashi and S. Nagase (Tokyo Metropolitan University)
5. Trimetallic Nitride Template (TNT) Endohedral Metallofullerenes 121
H. Dorn et al. (Virginia Polytech Institute and State University)
6. Redox properties and purification of endohedral metallofullerenes 133
M. Diener, M. Alford, and R. Bolskar (TDA Research Inc.)
7. Electron spin resonance spectroscopy for metallofullerenes 153
T. Kato (IMS)
8. Raman and infrared spectra of endohedral metallofullerenes 169
M. Krause and H. Kuzmany (Vienna University)
9. Structures of fullerides and endohedral metallofullerenes found by 185
MEM/Rietveld method
M. Takata et al. (Nagoya University)
10. Lanthanide-metallofullerenes 217
K. Kikuchi (Tokyo Metropolitan University)
v
vi TABLE OF CONTENTS
11. Chemical properties of endohedral metallofullerene and its ions 231
T. Akasaka, T. Wakahara et al. (Niigata University)
12. Encapsulation of atom into C cage 253
60
Y. Kubozono (Okayama University)
13. Endohedral metallofullerene in gas phase 273
S. Maruyama (University of Tokyo)
14. Capturer-captive chemistry. Endohedral fullerenes as representatives
of molecular jailing 295
T. Braun (Etovos University)
FOREWORD
To the eyes of a chemist, carbon is certainly one of the most fascinating elements
of the periodic table. Basically, the electronic structure and atomic size of carbon
enables this element to form a variety of bonds with other elements and, most
importantly, with other carbon atoms as weIl. These unique features lead to the
amazingly complicated molecular structures we encounter e.g. in life sciences and
organic chemistry. Of course, the technical importance of carbon is enormous -
but I don't want to carry too many coals to Newcastle. Prom the viewpoint of an
astrophysicist or chemist, the significance of carbon lies in the fact that it is the most
abundant condensable element in space. Born in the interior of stars, and from
there expelled into the interstellar medium, it initiates the formation of simple and
complex molecules and of nanoscopic grains. These in turn form huge clouds in
space - the birthplace of new stars and planetary systems. The decisive role of carbon
in interstellar chemistry is widely accepted and the search for more and more families
of interstellar carbon-bearing molecules is a topic of ongoing research.
The interdisciplinary aspect of carbon also concerns its various solid forms, in
which C and the other closed-cage fullerenes are certainly some of the most popular
60
newcomers. Trying to understand the formation of carbon molecules in space, Harry
Kroto in 1985 persuaded Bob Curl, Rick Smalley, and their students Jim Heath
and Sean O'Brien to the famous experiments leading to the discovery of C60, a
work which in 1996 was honored by the Noble price in chemistry. Shortly after
the discovery, these researchers devised a new experiment in order to obtain further
support for their revolutionary assumption of C having a soccer ball structure.
60
The basic idea was to do something which can only be accomplished in the case
C behaves like a hollow ball: to put something inside. These experiments were a
60
complete success, not only supporting the fullerene concept, but also giving birth
to endohedral fullerenes - as they are now called - a family of intriguing mole
cules which is the subject of this book.
I think this book is filling a gap - much has been written on fullerenes but
much less on their endohedral cousins. The usually very low efficiency of preparing
these species and the various frustrations experienced by researchers in the time
consuming separation and characterization work may be responsible for this situa
tion. Work on endohedrals is very hard and patient work indeed. But there is a
reward: since most elements of the periodic table - or even small clusters - should
potentially be encapsulated and thereby modify the chemical and physical proper
ties of the surrounding cage, certainly some very intriguing species may show up
or solids with exciting properties may be obtained. In addition, one may gain some
insight how endohedrals, and simultaneously, how fullerenes are formed - both
still not very weIl understood processes.
vii
viii FOREWORD
When in the early 1990s I attended a meeting in Berlin - Helmut Schwarz, who
coined the term "endohedral fullerenes" and at that time was pioneering the work
of gas phase helium - C6Q collisions, had organized a workshop at the very place
where about 250 years aga Leonhard Euler had published his famous theorem on
polyheders. There I met Martin Saunders, the father of the field of rare gas endo
hedrals. He was joking that in fact we had produced helium "endos" for the first
time, since we had used helium as quenching gas in our fullerene generator. With
reference to our previous experience with C it might have appeared that we again
60
had produced something without knowing! However, under standard conditions,
the yield of helium "endos" is so small (in the ppm range) that our oversight was
excusable.
Now let me turn briefly to the content of the book. Besides producing He@C
60
(this notation originates from Smalley, meaning that the unit left of @ is inside
the unit at the right), M. Saunders, J. Cross and coworkers also succeeded in
producing fullerenes containing other rare gas atoms, in particular the NMR active
3He. This helium acts as a kind of spectator allowing rather interesting investiga
tions of the interior and exterior of fullerenes. The joint article of B. Pietzak, A.
Weidinger, K.P. Dinse, and A. Hirsch concerns other fascinating species, namely
nitrogen and phosphor bearing C and C endohedrals. These species are usually
60 70
produced by implantation of the relevant atoms into bulk fullerene material.
Naturally, the yields in such processes are very low, but considerable progress in
preparation and characterization was made. The contribution of E.E.B. Campbell,
who pioneered in the implantation technique for producing endohedrals, concerns
the formation of alkali-C endos in gas-phase collisions and on coated C films.
6o 60
Further aspects of atom@C endohedral formation are covered by Y. Kubozono.
60
The most frequently applied endohedral production technique was introduced in
the early 1990s by Donald Bethune and coworkers from IBM, and employs a
fullerene generator in which the graphite electrodes are doped with the material to
be encapsulated, e.g. lanthanum or scandium. The various lanthanum endohedrals
produced by such a method are the subject of the article by K. Kikuchi. H. Dom
reports that a relatively small addition of nitrogen to the quenching gas opens the
door to a new class of endohedrals, in whieh small metal nitride clusters are encap
sulated. The detailed structure of endohedral compounds is the subject of the
theoretical works by K. Kobayashi and S. Nagase. Experimental methods to uncover
endohedral structures are of crucial importance. T. Kato presents his results based
on spin resonance techniques. Advanced X-ray diffraction methods are applied by
M. Takata, E. Nishibori, and M. Sakata. Of considerable analytical value is the
characterization of endohedrals by IR and Raman spectroscopy, by whieh e.g. the
vibration al motion of the encapsulated species should be discerned. This topic is
covered by H. Kuzmany and M. Krause. A further extremely important and still very
open field concerns the chemical properties of endohedrals, whieh may consider
ably differ from those of the empty fullerenes. Naturally, chemie al effects could
be applied for a more efficient purification and chromatographie separation. This
FOREWORD IX
issue plays a role in many of the articles presented here but is especially consid
ered in the contributions by M. Diener, M. Alford and R. Bolskar and in the work
of T. Wakahara, T. Akasaka, K. Kobayashi and S. Nagase. Gas phase studies of
endofullerenes is the field of S. Maruyama, who gives areport of his interesting
research. In chemistry, a molecular jail-like encapsulation or a more friendly host
guest relation is nothing new. How endohedral fullerenes are fitting into a general
scheme of enclosure compounds is elaborated by T. Braun in the final article.
My thanks to Takeshi Akasaka and Shigeru Nagase for the honor and oppor
tunity to write the foreword to this fascinating book. I am sure that the reader outside
the field will realize that endohedral fullerenes are an exciting and promising area
of research, while the specialists in the field will certainly gain new insights and
fruitful ideas.
Wolfgang Krätschmer
CHAPTER 1
PUTTING NONMETALS INTO FULLERENES
MARTIN SAUNDERS and R. JAMES CROSS
Yale Chemistry Department
P.O. Box 208107
New Haven. CT 05620-8107
USA
Key words: fullerene. endohedral, nonmetal, noble gas, NMR
Abstract: Three methods are described for putting atoms and small moleeules inside fullerenes:
heating the fullerene under high pressures of the gas, shooting in a beam of ions or fast atoms, or by
generating the atom at high kinetic energy in a nuclear reaction. Several applications are described.
NMR spectroscopy of 3He inside is a general and useful probe for studying fullerene chemistry.
1. Introduction
We have developed three methods to put atoms and small moleeules inside fullerene
eages. These systems are quite different from the metallofullerenes deseribed else
where in this volume. Metal atoms inside fullerenes are strongly bound to the earbon
eage, generally by an ionie bond. Nonmetal atoms are bound only by weak van
der Waals forees. They are stable beeause several earbon-earbon bonds must be
broken to free the atom. Metallofullerenes are generally made in a earbon are
using metal-doped graphite. We put the nonmetal atoms into an existing fullerene
moleeule. Beeause of the strong bonding, the ehemieal properties of metallo
fullerenes are quite different from those of the empty fullerene. In the nonmetal case,
the ehemisty and speetroseopy are very similar, and the included atom or mole eule
ean then be used to study the eleetronie properties of the empty fullerenes or as
an inert marker to study their reaetions. We deseribe below the methods of making
fullerenes eontaining nonmetals and then give several examples of how they ean
be used to study the strueture and reaetions of fullerenes. Reeent studies have shown
that fullerenes eontaining noble gases are found in nature assoeiated with eolli
sions of extraterrestrial objeets with the earth. These fullerene eompounds are
therefore beeoming important in geoehemistry and astroehemistry.
2. Methods of preparation
We have developed three methods to put atoms and small moleeules into fullerenes.
We ean heat the fullerenes in the presenee of the gas at high pressures. We ean
shoot the atoms inside using a beam of ions or fast atoms, or we ean generate the
T. Akasaka and S. Nagase (eds.), Endofullerenes, I-ll.
© 2002 Kluwer Academic Publishers.