Fullerene

With the advent of nanotechnology many new components and materials appeared to the world, one of such materials is fullerene. Fullerene is a molecule with total carbon composition and it is available in the form of tube, ellipsoid and hollow spheres. Cylinderical fullerenes are known as carbon nanotubes and spherical ones are called bucky balls. There structure is similar to the structure of graphite.

A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid or tube. Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.

Structure

Fullerenes consist of 20 hexagonal and 12 pentagonal rings as the basis of an icosahedral symmetry closed cage structure. Each carbon atom is bonded to three others and is sp2 hybridised. The C60 molecule has two bond lengths - the 6:6 ring bonds can be considered "double bonds" and are shorter than the 6:5 bonds. C60 is not "superaromatic" as it tends to avoid double bonds in the pentagonal rings, resulting in poor electron delocalisation. As a result, C60 behaves like an electron deficient alkene, and reacts readily with electron rich species. The geodesic and electronic bonding factors in the structure account for the stability of the molecule. In theory, an infinite number of fullerenes can exist, their structure based on pentagonal and hexagonal rings, constructed according to rules for making icosahedra.

Properties

The characteristics of fullerenes, both chemical and physical, have been the subject in the field of research since a long time now. Some restricted properties are still in use in the field of medical sciences for diagnosing cancer and bacteria in the living body. Some of the important characteristics of the fullerenes are listed below:

1. Aromaticity: Aromaticity is the reactivity of the certain material or molecule with other in the different temparature. Fullerene also has aromaticity in different situations. A spherical fullerene has pibonding electrons which are free to localize or delocalize in different chemical siuations. According to the Huckel’s rule the aromaticicty of fullerene is three dimentional. This property can be improved and managed according to the situation with the help of quantum chemical modelling which can empower the bonding. As a result, C60 in water tends to pick up two more electrons and become an anion.

    

2. Chemistry: According to the reseachers fullerenes are considered to be the stable molecules but not fully unreactive. In certain circumstances fullerene become reatcive. The reactive charatceristics of fullerene is electrophilic at double bonding, which reduces angle stress by changing hybridized carbons into sp3 hybridized ones. Due to the change in hybridized orbits, the bond angles tends to decrease from about 120° in orbitals of sp2 carbon atoms. This decrease in bond angles permits the bonds to bend lesser on closing the tube making fullerene molecule more stable.

    

3. Solubility: Fullerenes are soluble in various kinds of solvents. The most common solvents for the fullerenes include, carbon disulfide. Solutions of pure fullerene have a deep purple or voilet colour. Colour solutions of C70 are a reddish brown. The higher fullerenes from C76 to C84 have diferent colour according to the portion mixed with solvents. Fullerenes are the only present allotrope of carbon that have the property to get dissolved in common solvents at normal room temperature. But in some cases fullerene structures remain undissolved such as at their excite state these carbon allotropes are not soluble.

    

Uses*:*

Fullerenes are used in many applications because of their unique chemistry and, especially in materials science, electronics, and nanotechnology. Some famous examples are buckyball clusters, nanotubes, megatubes, polymers, nano onions and fullerene rings. All thses structures are used in fields of work to extract more imporved form of products from existing materials.

Safety and toxicity

When focusing on the toxic effects of the fullerene, it should be kept in mind that fullerene is not toxic in all forms. The physical bond of fullerene C60 is safe and non-toxic but the derivatives of fullerenes could be harmful to the health. Other fullerenes with covalently bonded chemical groups such as fullerene complexes, host-guest complexes, such as cyclodextrin are highly toxic. Aggregation of nano particles of C60, and C60 crystallites in much larger form encourages the toxicity.