19-1

Fullerenes: Properties

Fullerenes are important in nanoscience because they can be usedto form nanostructures. Either pure Carbon or modified.

C60: stable at room Temp and pressure

Shape is called a truncated octahedron

90 edges, 32 faces and 60 vertices (one for each carbon)

of the 32 faces: 12 are pentagons and 20 are hexagons

19-2

Euler's Theorem f + v = e +2

single bonds

double bonds

diameter = 7.10D

1.40D

1.46D

All carbons are equivalent

13C NMR (see CHEM 2070)

19-3Nuclear Magnetic Resonance

C70: see that the Carbons are of 5 types

19-4)H f0

C60 42.5kJ/mol C70 40.4 kJ/mol

19-5

Fullerene Synthesis

In Nature: high energy processes

We looked at these in lectures 13 and 14 (also see book chapter 4)

14-8

Arc Discharge

Developed in early 1980’s

Forms SWCNT as longAs catalyst is present

Rather dirtyMany unwanted products

19-6

Best method is by combustion of a hydrocarbon fuel at low pressure

-cleaner products

- requires less energy

Purification

A practical laboratory-scale method for purification of soot enriched in C60 and C70 starts with extraction in toluene followed by filtration. The solvent is evaporated and the residue (the toluene-soluble soot fraction) redissolved in toluene and subjected to column chromatography. C60 elutes first with a purple color and C70 is next displaying a reddish-brown color

19-7

Physical and Chemical Reactions of Fullerenes

Fullerenes are soft electrophiles

-accept electrons from a donor molecule -

e.g., hydrogen, methyl groups and amines

Three ways to modify Fullerenes

1. endohedral: --- encapsulate something inside it2. exohedral :-- react with surface3. assembly into bigger structures

19-8

as we saw in lectures 7 and 8C60 is fcc and has a nn dist of 10 D

balls rotate freely in solid state at RT

cohesive energy is about 1.5 eV(about 150 kJ/mol)

19-9

Exohedral Fullerenes

Fullerenes can be modified by chemical methods

19-10

Putting C60 on surfaces

note S linkage to gold -- very common method

C60 dimers

Further polymerization can occur

Double bonds on adjacent C60's are broken by laser or UV-light

undergo [2+2] cycloaddition reaction (see CHEM 2060 last lecture)

Rhombohedral, linear, tetragonal forms can be made

19-11

19-12

4. Carbon Nanotubes

We met these briefly before (lecture 12)

"bottom-up" synthesis

Two types: single walled carbon nanotubes SWCNT

multiwalled (MWCNT): Focus here is on SWCNT

19-13

STRUCTURE

Three main types: 1. Armchair 2. Zig-Zag and 3. Chiral

These are best introduced if we unroll a tube and lay it flat

roll this way : Armchair tube

zig-zagchiral

(called a graphene sheet)

apex of hexagon is parallel to longitudinal axis

apex of hexagon is parallel to circumference

19-14

Vector NotationMost nanotubes have the chiral form and are conveniently described using a vector notation.

The origin of the vector intersects two equivalent points (centre of a hexagon) on the graphene sheet.

In the figure the axes are shown for armchair and zigzag tubes: chiralaxis is sum of others

more next lecture

1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 10,0 11,0 12,0

1,1 1,1 3,1 4,1 5,1 6,1 7,1 8,1 9,1 10,1 11,1 12,1

2,2 3,2 4,2 5,2 6,2 7,2 8,2 9,2 10,2 11,2

3,3 4,3 5,3 6,3 7,3 8,3 9,3 10,3 11,3

4,4 5,4 6,4 7,4 8,4 9,4 10,4

5,5 6,5 7,5 8,5 9,5 10,5

0,0

6,6 7,6 8,6 9,6 10,6

7,7 8,7 9,7

Armchair

ZigzagChiralangle

13,1

12,2

12,3

11,4

11,5

7,7

10,6

13,0

8,7 9,7 10,7

8,8 9,8