Fullerene: Explanation, Structure, Types, Applications

In 1985, fullerene is discovered by a team of scientists Smalley, Kroto, and Curl. In 1996, they were awarded a Nobel prize in chemistry for the discovery of a new class of molecules. It was a great discovery because it boosted the knowledge of chemistry and physics due to its various applications in fields, such as astronomy, electronics, nanotechnology, material science, and medical science.

Fullerene is an allotrope of carbon and its molecule has carbon atoms that are bonded with each other by single and double bonds. The connectivity between the atoms of carbon gives a cage or ball-like structure of fullerene. This results in various shapes of fullerene, such as spheres, ellipsoids, tubes, etc.

The empirical formula of fullerene is denoted by C_n, where n is the number of carbon atoms. The most famous member of the fullerene family is buckminsterfullerene, denoted by the C₆₀. buckminsterfullerene (C₆₀) is a closed fullerene also known as buckyball due to its resemblance to football. Similarly, nested closed fullerene is called bucky onions while cylindrical fullerene is known as bucky tubes (carbon nanotubes).

Structure of fullerene

Fullerenes are highly stable and symmetrical molecules. They have a similar structure to graphite but the hexagonal rings are connected to the sheet in the form of a ball-like structure. Instead of hexagonal rings, they also have pentagonal and heptagonal ring structures. This arrangement of structure does not allow for the sheet of fullerene to be planar. Their structures depend on the type of modification, such as buckyball, buckytubes, etc. Fullerene exits in various forms depending on the number of carbon atoms, for instance, C₆₀, C₇₀, C₈₀, C₉₀, etc.

Types of fullerene

These are the types of fullerenes. Which are slightly different from each other in their properties and uses.

Buckyballs

Buckminsterfullerene is known as buckyball which is the smallest molecule of fullerene that contains pentagonal and hexagonal rings. The empirical formula of buckminsterfullerene is C₆₀, which means it has 60 carbon atoms in a single molecule of buckminsterfullerene. It can occur in nature and is found in soot.

The structure of buckminsterfullerene is truncated icosahedron, similar to football which has twenty hexagons and twelve pentagons. Each polygon and bond along each polygon edge has a carbon atom. The Van Der Waals diameter of the molecule is about 1.1 nanometers (nm) and the distance from the nucleus to the nucleus in the molecule is 0.71 nm.

There are two bond lengths of buckminsterfullerene molecule. One is the 6:6 bonds between the two hexagons rings are double bonds and the second is the 6:5 bonds between a hexagon and a pentagon. The second bond length is shorter than the first one and the average bond length is 1.4 Å.

buckyballs

Buckytubes

Carbon nanotubes are known as buckytubes. They are basically cylindrical fullerenes and have very short diameters. For instance, they can range from a few micrometers to millimeters in length and a few nanometers in width. They have both closed and open-ended structures.

fullerene buckytubes: carbon nanotubes

The molecular structures of buckytubes (carbon nanotubes) give a variety of uses due to their macroscopic properties. These includes

High tensile strength
High electrical conductivity
High ductility
High heat conductivity
Chemical inactivity

Heterofullerenes

Hetero fullerenes are discovered in 1993 and have extended the class of fullerenes. They have dangling bonds. They have heteroatoms that substitute the carbons in the tube or cage-shaped structures.

For example,

Boron
Nitrogen (azafullerene)
Oxygen
Phosphorus

Hybrid fullerenes

They exist between the buckyball and buckytubes. These are the main hybrid structure which are,

Carbon nanobuds
Buckybuds

Other fullerenes

These are the types of other fullerenes.

Fullerene C₂₀
Fullerene C₇₀
Fullerene C₇₂
Fullerene C₇₄
Fullerene C₇₆
Fullerene C₇₈
Fullerene C₈₄
Fullerene C₉₀
Fullerene C₃₉₉₆

Dodecahedral C₂₀ is the smallest fullerene. There are 1812 non-isomorphic fullerenes C₆₀ and the only one form of buckminsterfullerene has no pair of pentagons. Similarly, 214,127,713 non-isomorphic fullerenes C₂₀₀, 15,655,672 of which does not contain adjacent pentagons.

Derivatives of fullerenes

Buckyballs and buckytubes are used as a building blocks for their derivatives and larger structures. These are the examples of derivatives of fullerenes.

bucky onions
carbon mega tubes
Ball and chain dimers
Linked rings of buckyballs

Properties of fullerene

Fullerenes have physical and chemical properties due to their larger structures.

Physical properties

As the temperature of fullerene is increased, it converts into the next fullerenes. For example, C₆₀ converted into fullerene C₇₀.
They can change their structure under various pressure.
The ionization enthalpy of fullerene has 7.61 eV.
Fullerenes have an electron affinity between 26 to 2.8 eV.

Chemical properties

They are the most stable allotrope of carbon.
Fullerene act as an electrophile during a chemical reaction.
They are oxidizing agents and act as electron accepting groups.
fullerenes are superconductors.
They have the property of ferromagnetism.
Fullerenes show inherently chirality.
They are soluble in organic solvents like toluene and chlorobenzene.

Applications and uses of fullerene

Fullerenes are used in many applications in different fields. These are the uses and applications of fullerenes,

Fullerenes derivatives use in tumor research.
Used as a light-activated antimicrobial agent in the medical field.
Fullerenes are used in biomedical applications, such as high-performance MRI, X-ray imaging, and photodynamic therapy.
C₆₀ is used for drug delivery, lubricants, and catalysts.
They have the ability to work as conductors.
Fullerenes are also used as gas absorbents.
They are used for making fabrics and fibers based on buckytubes.
These are applicable to cosmetic products.
They are also used in photovoltaic applications.
Fullerenes are used in organic solar cells.

Concepts Berg

What Makes Fullerene Acceptors Special as Electron Acceptors in Organic Solar Cells and How to Replace Them?

Low-level excited states of the fullerene ions such as anions, increase charge separation in organic solar cells containing fullerene derivatives as electron acceptors.

Is fullerene stronger than a diamond?

Under high pressure, it is stronger than a diamond. Otherwise, it is soft.

How is fullerene made?

They are made of fullerene-rich soot. A high voltage of current passes through the molecules and it vaporizes the carbon into plasma then it cools into soot residues.

Where is fullerene found?

It is an allotrope of carbon and is found naturally in soot.

Why is fullerene an antioxidant?

Because they can inactivate the hydroxyl free radicals by attaching to double bonds.

What is the dangling bond in fullerene?

A dangling bond is an unsatisfied valency on an immobilized atom. Such kinds of atoms are known as immobilized free radicals.

Why is fullerene a good lubricant?

Fullerenes are acting as nanoparticles and are inserted between the friction area easily, where they increase viscosity and prevent the contact of metals with each other

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