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Carbon Structures
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Modifikationen des Kohlenstoff
Diamant

• Kohlenstoffatome auf Tetraederplätzen
• sp3-Hybridisierung
• sehr rigides C-Gerüst,
• (Bindungslänge 1.54 Å)
• Transparent
• Isolator
• (5.5 eV Bandlücke)

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Graphit

• Struktur aus hexagonalen Schichten
• sp2 - Hybridisierung
• starke C-C Bindung in Ebene (1.42 Å)
• schwache Kopplung benachbarter Ebenen
• (Abstand 3.35 Å)
• Verwendung zum Schreiben, als Gleitmittel
• Halbmetall, Elektronentransport in Ebenen

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Neue Materialien aus Kohlenstoff

• 1985 Kroto, Heath, OBrien, Curl Smalley
• Laserverdampfung von Graphit

30 mJ NdYAG
10 atm He
TOF-MS
PHe 760 Torr
rot. Graphitscheibe
PHe 10 Torr

• Massenspektrometrie
• Aggregate aus 60 C

• Kohlenstoffgerüst analog Fussballtopologie

Kroto et al., Nature 318 (1985) 162
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Fullerene

• C60 und verwandte Strukturen
• erinnern an Architektur von
• Buckminster Fuller
• Buckminsterfullerene,
• Buckyballs,
• allg. Fullerene

Buckminster Fuller vor geodätischem
Dom (amerikanischer Pavillon, Montreal 1967) Juni
1954 U.S. Patent No. 2,682,235
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C60 und verwandte Spezies

• Familie der Fullerene
• C60, C70, C260, C960
• 1990 Krätschmer und Huffmann
• Entdeckung von C60 in der Asche
• einer Bogenentladung
• Massenproduktion!

Van der Waals Kristalle aus C60 (fcc Struktur)
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Atomorbitale
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bonding
Molecular Orbitals
antibonding
antibonding
bonding
bonding
antibonding
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H2O
NH3
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sp2
sp3
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sp
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C2H6
CH4
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?-bond
C2H4
?-bond
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C2H2
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delocalized ?-electrons
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Benzene C6H6
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Carbon Clusters
Mass spectrum produced by laser vaporization
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Small Carbon Clusters
mass spectrum
electron affinity
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The Fullerene Family
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C60
C70
a This value was obtained from NMR measurements.
The calculated geometric value for the diameter
is 7.09 Å (see text). b This value for the outer
diameter is found by assuming the thickness of
the C60 shell to be 3.35 A. In the solid, the C60
- C60 nearest-neighbor distance is 10.02 Å (see
Table 7.1). c The binding energy for CM is
believed to be 0.7 eV/C atom less than for
graphite, though literature values for both are
given as 7.4 eV/C atom. The reason for the
apparent inconsistency is attributed to
differences in calculational techniques. d
Literature values for the optical absorption edge
(see 13.2.1) for the free C60 molecules in
solution range between 1.55 and 2.3 eV.
a Values for the eight distinct bond lengths are
given in Table 3.3. b The volume of the C70
molecule is defined as V ?abc, where a,b,c
denote the radii of the ellipsoid as given in
this table. c The calculated binding energy per C
atom is 20 meV greater for C70 than for C60 and
690 meV less than for graphite, but the absolute
magnitude of the binding energy is less
certain. d The calculated band gap varies from
1.55 eV 3.49 to 1.76 eV 3.51.
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Formation of the Fullerenes
NMR spectra
C60 one single line
ppm
C70 four lines
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Bucky balls as bouncing balls
Inside or outside ?
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Clusters of C60
Icosaeder !
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Crystals of C60