Nobel prize in chemistry 1996

From nobelsrv@www.nobel.ki.seWed Oct  9 19:00:59 1996
Date: Wed, 9 Oct 1996 15:37:04 +0100
From: Nobel Foundation WWW Server 

Kungl. Vetenskapsakademien
The Royal Swedish Academy of Sciences
Box 50005, S-104 05 Stockholm, Sweden. Ph: +46 8 673 95 00,
fax: +46 8 15 56 70, e-mail: rsas@kansli.kva.se

The Royal Swedish Academy of Sciences has decided to award
the 1996 Nobel Prize in Chemistry jointly to

Professor Robert F. Curl, Jr., Rice University, Houston, USA,
Professor Sir Harold W. Kroto, University of Sussex, Brighton,
U.K., and
Professor Richard E. Smalley, Rice University, Houston, USA,

for their discovery of fullerenes.

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The discovery of carbon atoms bound in the form of a ball is
rewarded
New forms of the element carbon - called fullerenes - in which
the atoms are arranged in closed shells was discovered in 1985
by Robert F. Curl, Harold W. Kroto and Richard E. Smalley. The
number of carbon atoms in the shell can vary, and for this
reason numerous new carbon structures have become known.
Formerly, six crystalline forms of the element carbon were
known, namely two kinds of graphite, two kinds of diamond,
chaoit and carbon(VI). The latter two were discovered in 1968
and 1972.

Fullerenes are formed when vaporised carbon condenses in an
atmosphere of inert gas. The gaseous carbon is obtained e.g. by
directing an intense pulse of laser light at a carbon surface.
The released carbon atoms are mixed with a stream of helium gas
and combine to form clusters of some few up to hundreds of
atoms. The gas is then led into a vacuum chamber where it
expands and is cooled to some degrees above absolute zero. The
carbon clusters can then be analysed with mass spectrometry.

Curl, Kroto and Smalley performed this experiment together with
graduate students J.R. Heath and S.C. O9Brien during a period of
eleven days in 1985. By fine-tuning the experiment they were
able in particular to produce clusters with 60 carbon atoms and
clusters with 70. Clusters of 60 carbon atoms, C60, were the
most abundant. They found high stability in C60, which suggested
a molecular structure of great symmetry. It was suggested that
C60 could be a "truncated icosahedron cage", a polyhedron with
20 hexagonal (6-angled) surfaces and 12 pentagonal (5-angled)
surfaces. The pattern of a European football has exactly this
structure, as does the geodetic dome designed by the American
architect R. Buckminster Fuller for the 1967 Montreal World
Exhibition. The researchers named the newly-discovered structure
buckminsterfullerene after him.

The discovery of the unique structure of the C60 was published
in the journal Nature and had a mixed reception - both criticism
and enthusiastic acceptance. No physicist or chemist had
expected that carbon would be found in such a symmetrical form
other than those already known. Continuing their work during
1985-90, Curl, Kroto and Smalley obtained further evidence that
the proposed structure ought to be correct. Among other things
they succeeded in identifying carbon clusters that enclosed one
or more metal atoms. In 1990 physicists W. Kratschmer and D.R.
Huffman for the first time produced isolable quantities of C60
by causing an arc between two graphite rods to burn in a helium
atmosphere and extracting the carbon condensate so formed using
an organic solvent. They obtained a mixture of C60 and C70, the
structures of which could be determined. This confirmed the
correctness of the C60 hypothesis. The way was thus open for
studying the chemical properties of C60 and other carbon
clusters such as C70, C76, C78 and C84. New substances were
produced from these compounds, with new and unexpected
properties. An entirely new branch of chemistry developed, with
consequences in such diverse areas as astrochemistry,
superconductivity and materials chemistry/physics.

Background
Many widely diverse research areas coincide in the discovery of
the fullerenes. Harold W. Kroto was at the time active in
microwave spectroscopy, a science which thanks to the growth of
radioastronomy can be used for analysing gas in space, both in
stellar atmospheres and in interstellar gas clouds. Kroto was
particularly interested in carbon-rich giant stars. He had
discovered and investigated spectrum lines in their atmospheres
and found that they could be ascribed to a kind of long-chained
molecule of only carbon and nitrogen, termed cyanopolyynes. The
same sort of molecules is also found in interstellar gas clouds.
Kroto's idea was that these carbon compounds had been formed in
stellar atmospheres, not in clouds. He now wished to study the
formation of these long-chain molecules more closely.

He got in touch with Richard E. Smalley, whose research was in
cluster chemistry, an important part of chemical physics. A
cluster is an aggregate of atoms or molecules, something in
between microscopic particles and macroscopic particles. Smalley
had designed and built a special laser-supersonic cluster beam
apparatus able to vaporise almost any known material into a
plasma of atoms and study the design and distribution of the
clusters. His paramount interest was clusters of metal atoms,
e.g. metals included in semiconductors, and he often performed
these investigations together with Robert F. Curl, whose
background was in microwave and infra-red spectroscopy.

Atoms form clusters
When atoms in a gas phase condense to form clusters, a series is
formed where the size of the clusters varies from a few atoms to
many hundreds. There are normally two size maxima visible in the
distribution curve, one around small clusters and one around
large. It is often found that certain cluster sizes may
dominate, and the number of atoms in these is termed a "magic
number", a term borrowed from nuclear physics. These dominant
cluster sizes were assumed to have some special property such as
high symmetry.

Fruitful contact
Through his acquaintanceship with Robert Curl, Kroto learned
that it should be possible to use Smalley's instrument to study
the vaporisation and cluster formation of carbon, which might
afford him evidence that the long-carbon-chain compounds could
have been formed in the hot parts of stellar atmospheres. Curl
conveyed this interest to Smalley and the result was that on 1
September 1985 Kroto arrived in Smalley's laboratory to start,
together with Curl and Smalley, the experiments on carbon
vaporisation. In the course of the work it proved possible to
influence drastically the size distribution of the carbon
clusters where, predominantly, 60 appeared as a magic number but
also 70. The research group now got something else to
think about. Instead of long carbon chains, the idea arose that
the C60 cluster could have the structure of a truncated (cut
off) icosahedron since its great stability was assumed
to correspond to a closed shell with a highly symmetrical
structure. C60 was given a fanciful name, buckminsterfullerene,
after the American architect R. Buckminster Fuller, inventor of
the geodesic dome. This hectic period ended on 12 September with
the despatch of a manuscript entitled C60: Buckminsterfullerene
to Nature. The journal received it on 13 September and published
the article on 14 November 1985.

Sensational news
For chemists the proposed structure was uniquely beautiful and
satisfying. It corresponds to an aromatic, three-dimensional
system in which single and double bonds alternated, and was thus
of great theoretical significance. Here, moreover, was an
entirely new example from a different research tradition with
roots in organic chemistry: producing highly symmetrical
molecules so as to study their properties. The Platonic bodies
have often served as patterns, and hydrocarbons had already been
synthesised as tetrahedral, cubic or dodecahedral (12-sided)
structures.

Further investigations
To gain further clarity Curl, Kroto and Smalley continued their
investigations of C60. They attempted to make it react with
other compounds. Gases such as hydrogen, nitrous oxide, carbon
monoxide, sulphur dioxide, oxygen or ammonia were injected into
the gas stream, but no effect on the C60 peak recorded in the
mass spectrometer could be demonstrated. This showed that C60
was a slow-reacting compound. It also turned out that all carbon
clusters with an even number of carbon atoms from 40-80 (the
interval that could be studied) reacted equally slowly.
Analogously with C60 all these should then correspond to
entirely closed structures, resembling cages. This was in
agreement with Euler's law, a mathematical proposition which
states that for any polygon with n edges, where n is an even
number greater than 22, at least one polyhedron can be
constructed with 12 pentagons and (n-20)/2 hexagons, which, in
simple terms, states that it is possible with 12 pentagons and
with none or more than one hexagon to construct a polyhedron.
For large n many different closed structures can occur, thus
also for C60, and it was presumably the beautiful symmetry of
the proposed structure that gave it the preference.

The combination of chemical inertia in clusters with even
numbers of carbon atoms and the possibility that all these could
possess closed structures in accordance with Euler's law, led to
the proposal that all these carbon clusters should have closed
structures. They were given the name fullerenes and conceivably
an almost infinite number of fullerenes could exist. The element
carbon had thus assumed an almost infinite number of different
structures.

C60 and metals
New experiments were rapidly devised to test the C60 hypothesis.
Since the C60 structure is hollow, with room for one or more
other atoms, attempts were made to enclose a metal atom. A
graphite sheet was soaked with a solution of a metal salt
(lanthanum chloride, LaCl3) and subjected to
vaporisation-condensation experiments. Masspectroscopic analysis
of the clusters formed showed the presence of C60La+. These
proved to be photoresistant, i.e. irradiation with intense laser
light did not remove the metal atoms. This reinforced the idea
that metal atoms were captured inside the cage structure.

The possibility of producing clusters with a metal atom enclosed
gave rise to what was termed the "shrink-wrapping" experiment.
Ions of one and the same size or at least similar sizes were
gathered in a magnetic trap and subjected to a laser pulse. It
then turned out that the laser beam caused the carbon cage to
shrink by 2 carbon atoms at a time: at a certain cage size, when
the pressure on the metal atom inside became too great, the
fragmentation ceased. The shell had then shrunk so that it
fitted exactly around the metal atom. For C60Cs+ this size was
at C48Cs+, for C60K+ it was at C44K+ and for C60+ at C32+.

Further strong evidence gave rise to new chemistry
At the end of the 1980s, strong evidence was available that the
C60 hypothesis was correct. In 1990 the synthesis of macroscopic
quantities of C60 through carbon arc vaporisation between two
graphite electrodes permitted the attainment of full certainty -
the whole battery of methods for structure determination could
be applied to C60 and other fullerenes and completely confirmed
the fullerene hypothesis. As opposed to the other forms of
carbon the fullerenes represent well-defined chemical compounds
with in some respects new properties. A whole new chemistry has
developed to manipulate the fullerene structure, and the
properties of fullerenes can be studied systematically. It is
possible to produce superconducting salts of C60, new
three-dimensional polymers, new catalysts, new materials and
electrical and optical properties, sensors, and so on. In
addition, it has been possible to produce thin tubes with closed
ends, nanotubes, arranged in the same way as fullerenes. From a
theoretical viewpoint, the discovery of the fullerenes has
influenced our conception of such widely separated scientific
problems as the galactic carbon cycle and classical aromaticity,
a keystone of theoretical chemistry. No practically useful
applications have yet been produced, but this is not to be
expected as early as six years after macroscopic quantities of
fullerenes became available.

Further reading
Jim Baggott, Perfect Symmetry: The Accidental Discovery of
Buckminsterfullerene, Oxford University Press, 1994, IX + 315
pp.
Hugh Aldersey-Williams, The Most Beautiful Molecule: An
Adventure in Chemistry, Aurum Press, London, 1995, IX + 340 pp.
Robert F. Curl and Richard E. Smalley, Probing C60, Science, 18
Nov. 1988 Vol. 242
Harold Kroto, Space, Stars, C60, and Soot, Science, 25 Nov. 1988
Vol. 242
H.W. Kroto, A.W. Allaf, and S.P. Balm, C60:
Buckminsterfullerene, American Chemical Society, 1991
Richard E. Smalley, Great Balls of Carbon; The Story of
Buckminsterfullerene, The Sciences, March/April 1991
The All-Star of Buckyball; Profile: Richard E. Smalley,
Scientific American, September 1993
Rudy M. Baum, Commercial Uses of Fullerenes and Derivatives Slow
to Develop, News Focus, Nov. 22, 1993 C&EN
Hargittai, Istvan, Discoverers of Buckminsterfullerene, The
Chemical Intelligencer, Springer-Verlag, New York, 1995

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Robert F. Curl Jr., was born in 1933 in Alice, Texas, USA: Ph.D.
in chemistry in 1957 at University of California, Berkeley, USA.
Curl has since 1958 worked at Rice University, where he has been
a professor since 1967.

Professor Robert F. Curl Jr.
Department of Chemistry
Rice University
P.O. Box 1892
Houston, TX 77251, USA

Sir Harold W. Kroto was born in 1939 in Wisbech, Cambridgeshire,
UK. He obtained his Ph.D. in 1964 at the University of
Sheffield, UK. In 1967 he moved to the University of Sussex,
where he still works. In 1985 he became Professor of Chemistry
there and in 1991 Royal Society Research Professor.

Professor Sir Harold W. Kroto
School of Chemistry and Molecular Sciences
University of Sussex
Brighton, Sussex BN1 9QJ, UK

Richard E. Smalley was born in 1943 in Akron, Ohio, USA. Ph.D.
in chemistry 1973 at Princeton University, USA. Professor of
Chemistry at Rice University since 1981 and also Professor of
Physics at the same university since 1990. Member of the
National Academy of Sciences in the USA and other bodies.

Professor Richard E. Smalley
Department of Chemistry
Rice University
P.O. Box 1892
Houston, TX 77251, USA

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