Chemistry of Fullerenes

Fullerenes: Preparation, Properties, Structure, Bonding and Uses

NEET • JEE Main • JEE Advanced • GATE • CSIR-NET • IIT-JAM • State PSC

1. Discovery & Introduction

• Discovered in 1985 by Harold Kroto, Robert Curl, Richard Smalley
• Nobel Prize in Chemistry 1996
• C₆₀ named Buckminsterfullerene after architect Buckminster Fuller (geodesic dome structure)
• Colloquially called “Buckyball”

2. Structure of Fullerenes

• Hollow cage-like molecules made entirely of carbon
• Most stable & common: C₆₀ (Buckminsterfullerene)
• C₆₀: Truncated icosahedron → 12 pentagons + 20 hexagons (soccer ball shape)
• Each carbon is sp² hybridized but with slight pyramidalization
• Bond length: Pentagon–hexagon edge ≈ 1.45 Å, hexagon–hexagon ≈ 1.39 Å
• All carbon atoms are equivalent in C₆₀
• Other common fullerenes: C₇₀, C₇₆, C₈₄, etc.
• Endohedral fullerenes: Metal atoms trapped inside cage, e.g., La@C₈₂

JEE Advanced favourite: C₆₀ has 12 pentagons and 20 hexagons → Euler’s formula satisfied.

Structure of Fullerenes

3. Preparation of Fullerenes

Method	Description	Key Points
Arc Discharge Method (Krätschmer–Huffman)	Electric arc between two graphite electrodes in He atmosphere (0.1–1 atm) → Soot collected → extracted with benzene/toluene	▪ Most common lab method ▪ Yield: C60 ~10–15%, C70 ~2–5% ▪ Standard method in exams
Laser Vaporisation	Original method by Kroto et al. (1985)	Discovery method
Combustion Method	Controlled burning of benzene + oxygen	Industrial scale possible

Most asked: Fullerenes are produced by arc discharge between graphite electrodes in inert atmosphere.

4. Properties of C₆₀ (Buckminsterfullerene)

Property	Value / Nature	Reason
Appearance	Black solid (pure), Magenta in solution	Conjugation
Melting point	Sublimes at ~600°C	Weak van der Waals forces
Solubility	Insoluble in water, soluble in benzene, CS₂, toluene	Non-polar
Electrical conductivity	Insulator (pure), becomes conductor when doped with alkali metals (superconductor)	e.g., K3C60 → Tc = 19 K
Density	1.72 g/cm³	Hollow cage
Aromaticity	Highly aromatic (spherical aromaticity)	60 π-electrons delocalised over sphere

CSIR-NET/GATE: Alkali metal doped C₆₀ (A₃C₆₀) shows superconductivity (highest T_c = 40 K for Cs₃C₆₀ under pressure).

5. Chemical Reactions of Fullerenes

• Electrophilic addition → behaves like electron-deficient alkene
• Forms adducts with cyclopentadiene (Diels–Alder)
• Hydrogenation: C₆₀H₆₀ possible
• Halogenation: C₆₀F₆₀ (most fluorinated)
• Forms fullerides with alkali metals (e.g., K₃C₆₀)
• Osmylation, amination, polymerisation possible
• Endohedral complexes: N@C₆₀, He@C₆₀

NEET/JEE: Fullerenes undergo electrophilic addition reactions due to electron-deficient double bonds.

6. Uses & Applications of Fullerenes

1. Superconductors: A₃C₆₀ (A = K, Rb, Cs)
2. Organic solar cells (PCBM derivatives)
3. Drug delivery & medicinal chemistry (water-soluble derivatives)
4. Antioxidants (radical scavengers – “buckyball sponge”)
5. Catalysts & hydrogen storage
6. Nanotechnology (building block for nanotubes, graphene)
7. Lubricants (ball-bearing-like motion)
8. Endohedral fullerenes in quantum computing (N@C₆₀)

JEE Main 2024 asked: “Fullerene derivatives are used in organic photovoltaic cells.”

7. Comparison of Carbon Allotropes (High Weightage)

Property	Diamond	Graphite	Fullerene (C60)	Graphene
Hybridisation	sp³	sp²	sp² (curved)	sp²
Dimensionality	3D	2D layers	0D (molecule)	2D sheet
Hardness	Hardest	Soft	Soft	Very strong
Conductivity	Insulator	Conductor	Insulator → superconductor when doped	Best conductor
Discovery	Ancient	Ancient	1985	2004

Must Read Fullerenes MCQs asked in NEET ▪ JEE Main & Advanced ▪ JAM ▪ GATE ▪ CSIR-NET ▪ State PSC

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