The inorganic chemistry of Carbon

Carbon Nano tubes Graphite intercalated compounds

Graphene

Fullerenes

In 1985, Harold Kroto (Sussex), Robert Curl and Richard Smalley, (Rice

University,) discovered C 60 , and shortly thereafter came to discover the fullerenes. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of H. Kroto R. Smalley molecules. C 60 and other fullerenes were later noticed occurring outside the laboratory (for example, in normal candle-soot).. Fullerenes An idea from outer space Kroto's special interest in red giant stars rich in carbon led to the discovery of the fullerenes. For years, he had had the idea that long- chained molecules of carbon could form near such giant stars. To mimic this special environment in a laboratory, Curl suggested contact with Smalley who had built an apparatus which could evaporate and analyze almost any material with a laser beam. During the crucial week in Houston in 1985 the Nobel laureates, together with their younger co- workers J. R. Heath and J. C. O'Brien, starting from graphite, managed to produce clusters of carbon consisting mainly of 60 or 70 carbon atoms. These clusters proved to be stable and more interesting than long-chained molecules of carbon. Two questions immediately arose. How are these clusters built? Does a new form of carbon exist besides the two well-known The read-out from the mass spectrometer shows forms graphite and diamond? how the peaks corresponding to C 60 and C70 become more distinct when the experimental conditions are optimized. C60 is soccer-ball-shaped or Ih with 12 pentagons and 20 hexagons. According to Euler's theorem these 12 pentagons are required for closure of the carbon network consisting

of n hexagons and C 60 is the first stable fullerene because it is the smallest possible to obey this rule (higher ones C 180, 540). In this structure none of the pentagons make

contact with each other. Both C 60 and its relative C 70 obey this so-called isolated pentagon rule (IPR) . Non-IPR fullerenes have thus far only been isolated as endohedral

fullerenes such as Tb 3N@C 84

The double bonds in fullerene are not all the same. Two groups can be identified: 30 so- called [6,6] double bonds connect two hexagons and 60 [5,6] bonds connect a hexagon and a pentagon. Of the two the [6,6] bonds are shorter with more double-bond character and therefore a hexagon is often represented as a cyclohexatriene and a pentagon as a pentalene or [5]radialene. In other words, although the carbon atoms in fullerene are all conjugated the superstructure is not a super aromatic compound. The X-ray diffraction bond length values are 135.5 pm for the [6,6] bond and 146.7 pm for the [5,6] bond. Preparation and purification of C60 and C70

Kratschmer’s methodology for preparation of fullerenes is the one widely used currently which has been modified by various workers to increase yields. It was Kroto again who separated C60 and C70 for the first time in pure forms. Graphite electrodes are evaporated in an atmosphere of ~ 100 torr of Helium (Kratschmer) or 50 -100 torr of Argon (Kroto) in a glass vessel (modified RB flask, Power from a transformer) . The soot formed is scrapped and dispersed in benzene whereupon a wine red solution is obtained. This is filtered from the insoluble solids and concentrated . This mixture of C60 and C70 is then run on an alumina column using hexane as eluant. The magneta colored C60 elutes out first followed by the port wine colored C70 . In a typical case the ratio of C60 to C70 will be 5:1. Solid pure C60 will be mustard colored [UV 596 , 604 , 625 nm] and C70 will be red [600, 617, 644 nm]. (laser vaporization of graphite and graphite doped with other elements and compounds such as lanthanide metals, boron nitride has also been used for synthesis of fullerenes ) How to draw a C60?

step 1 step 2 step 3 step 4 step 5 ( no double bonds in pentagons)

The structure of C60 can be specifically described as having 12 pentagons and 20 hexagons with the pentagons sharing no common edge and the hexagons sharing edges with another hexagon or a pentagon. All the carbons are tricoordinate, pyramidal and all pentagons and hexagons are planar. Two types of C- C bonds are present in the molecule with differing bond lengths, 1.388 Å for a 6,6 bond (common for two hexagons) and 1.432 Å for a 5,6 bond (common for a hexagon and a pentagon ).

In contrast to C60 were all carbon atoms are identical, C70 has five different types of carbon atoms depending on the carbon environment. These are easily 13 differentiated by C NMR. C76 , another fullerene whose X ray structure has been solved belongs to D2 point group, is chiral and occurs as a racemic mixture. Stability of C 60

( a ) ( b) (c)

The unusual stability of C60 compared to other higher / lower fullerenes has been explained. In the structure of C60 , all the twelve pentagons are isolated from each other. Again only in C60 we can see double bonds arranged in such a way that they are located only in six membered rings and none in five membered rings. This is favored as there will be less strain on the already strained five membered rings as a result of such an arrangement. The need to avoid double bonds in pentagons largely governs the stability of fullerenes as the five membered rings with five planar hexagons around are already strained and unsaturation is going to increase the strain further. C60 has only arrangement (a) in its structure while C70 and C84 has five and six of the (b) arrangements in their structures respectively. Concept of aromaticity on C60

Initially C60 was predicted to be extremely stable and aromatic. Even more than 12,500 resonance structures were proposed. The terms superaromaticity and three dimensional aromaticity were freely used to describe its structure. However the presence of strained five membered rings adjacent to benzenoid rings were overlooked. Only one structure exists for C60 which avoids having any double bonds in pentagons. The two important consequences of this finding was that a) the delocalization of electrons in C60 is poor and so it is more reactive than expected. b) C60 is not so much an aromatic compound and the double bonds in it are isolated. This is clearly indicated by the η2 coordination shown by C60 when reacted with Vaska’s complex Chemistry of fullerenes: Different directions

Twenty-nine years on

from the discovery of C 60 , the outstanding properties and potential applications of the synthetic carbon allotropes — fullerenes, nanotubes and graphene — overwhelmingly illustrate their unique scientific and technological importance.

a, Fullerene salts; b, exohedral adducts/derivatives; c, open-cage fullerenes; d, quasi-fullerenes; e, heterofullerenes; f, endohedral fullerenes. Endohedral and open cage

Molecular Surgery!

The molecular surgery technique involves a series of carefully controlled chemical reactions to open up the fullerene cage and then insert the guest molecule into the fullerene cage through high temperature and pressure condition. It then follows up with another series of reaction to reseal the orifice while the molecule is inside. This is the technique used to synthesize all variant of dihydrogen endofullerenes Exohedral Fullerenes

ηηη2 – Complexes of fullerenes

OC CO OC CO OC Ru CO Ru CO OC Ru CO ηηη5- Complexes of Fullerenes Bucky metallocenes Lewis acidity of Fullerene: Reaction with an N Heterocyclic carbene Different dimensionalities of carbon materials

Graphene is a 2D building material for different dimensionalities of carbon materials, can be wrapped into fullerenes, rolled into nanotubes or stacked into graphite Carbon Nanotubes

The first observation of the multiwalled carbon nanotubes was credited to Iijima. In 1993 Iijima and Donald Bethune found single walled nanotubes known as buckytubes. This helped the scientific community make more sense out of not only the potential for nanotube research, but the use and existence of fullerene.

Nanotubes discovered in the soot of arc discharge at NEC, by Japanese researcher Sumio Iijima Nano

10 -9 10 -6 10 -3 10 0 10 3 10 6 10 9 m

• Size – 10 -9 m (1 nanometer) • Border to quantum mechanics What are Carbon nanotubes?

•Carbon nanotubes (CNTs ) are allotropes of carbon. These cylindrical carbon molecules have interesting properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential SWNT uses in architectural fields.

•They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Their final usage, however, may be limited by their potential toxicity.

MWNT Nanotube Three types based on style of roll formation ZIG ZAG , ARM CHAIR , CHIRAL Nanotube

High aspect ratio: Length: length >1000 typical few μm diameter → quasi 1D solid

The shortest carbon nanotube is the organic compound cycloparaphenylene, having 8 phenyl rings connected Diameter: through para positions which was synthesized in early as low as 1 nm 2009

The longest carbon nanotubes grown so far are over 550 mm long was reported in 2013 Electrical Properties Electrical conductance depending on helicity

• If the nanotube structure is armchair then the electrical properties are metallic • If the nanotube structure is chiral then the electrical properties can be either semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor • In theory, metallic nanotubes can carry an electrical current density of 4×10 9 A/cm 2 which is more than 1,000 times greater than metals such as copper Mechanical Properties

Strong Like Steel

Light Like Aluminum

Elastic Like Plastic Strength Properties • Carbon nanotubes have the strongest tensile strength of any material known. • It also has the highest modulus of elasticity .

Young's Modulus Tensile Strength Elongation at Material (TPa) (GPa) Break (%) SWNT ~1 (from 1 to 5) 13-53 E 16 Armchair 0.94 T 126.2 T 23.1 SWNT Zigzag SWNT 0.94 T 94.5 T 15.6-17.5 Chiral SWNT 0.92 MWNT 0.8-0.9 E 150 Stainless Steel ~0.2 ~0.65-1 15-50 Kevlar ~0.15 ~3.5 ~2 Kevlar T 0.25 29.6

YM is a measure of the stiffness of an elastic material TS is the maximum stress a material can take Yarn

Zhang, Atkinson and Baughman, Science 306 (2004) 1358. Yarn

MWCNT • Operational -196 oC < T < 450 oC • Electrical conducting • Toughness comparable to Kevlar • No rapture in knot

Zhang, Atkinson and Baughman, Science 306 (2004) 1358. Commercial

• Companies: ~ 20 worldwide - Carbon Nanotechnologies Inc. (CNI) - SES Research - n-Tec • Prices: - Tubes: pure SWCNT $500 / gram (CNI) MWCNT € 20-50 / gram (n-Tec)

-C60 : pure $100-200 / gram (SES Research) - Cones: Multi € 1 / gram (n-Tec)

- Gold : $10 / gram Graphene

Sir Novoselov Sir Andre Geim

Andre Geim was awarded the 2010 Nobel Prize in Physics jointly with Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene". Graphene consists of one-atom-thick layers of carbon atoms arranged in two-dimensional hexagons, and is the thinnest material in the world, as well as one of the strongest and hardest. The material has many potential applications and is considered a superior alternative to silicon. Geim's achievements include the discovery of a simple method for isolating single atomic layers of graphite, known as graphene using scotch tape. The team published their findings in October 2004 in Science Graphene

2 dimensional material , 1 atom thick Thinnest object: 1million times than hair Lightest object Strongest material, 300 times stronger than steel Flexible, stretchable and bendable Harder than diamond Conducts electricity better than copper and silver Conducts heat better than diamond Transparent Graphene: thermal properties compared

Thermal conductivity Material W/( m·K) Silica Aerogel 0.004 - 0.04 Air 0.025 Wood 0.04 - 0.4 Water (liquid) 0.6 Glass 1.1 Soil 1.5 Concrete , stone 1.7 Ice 2 Sandstone Stainless steel 12.11 ~ 45.0 Lead 35.3 Gold 318 Copper 401 Silver 429 Diamond 900 - 2320 Graphene (4840 ±440) - (5300 ±480) Preparation and characterization graphene

Preparation methods

Top-down approach Bottom up approach (From graphite) (from carbon precursors)

- Micromechanical exfoliation of graphite (Scotch - By chemical vapour deposition (CVD) tape or peel-off method) of hydrocarbon - Creation of colloidal suspensions from graphite - By epitaxial growth on electrically oxide or graphite intercalation compounds (GICs ) insulating surfaces such as SiC - Total Organic Synthesis

Ref: Carbon, 4 8, 2 1 2 7 –2 1 5 0 ( 2 0 1 0 ) Preparation methods

Top-down approach (From graphite)

Direct exfoliation of From Graphite Graphite oxide graphite intercalation method compounds Direct exfoliation of graphite

Graphene sheets ionic-liquid-modified by electrochemistry using graphite electrodes.

Liu, N. et al. One-step ionic-liquid-assisted electrochemical synthesis of ionicliquid- functionalized graphene sheets directly from graphite. Adv. Funct. Mater. 18, 1518–1525 (2008). Graphite intercalation compound

J. Mater. Chem. 2005, 15, 974. Graphite oxide method (Most common and high yield method)

Oxidation (Hummers’method) Graphite Oxide

H2SO 4/ KMnO 4 H2SO 4/KClO 3 Graphite Or H2SO 4/HNO 3 ………………. H2O

Ultrasonication (exfoliation)

Fuctionalization (for better dispersion ) Graphene Oxide monolayer or few layers

Chemical reduction to restore graphitic structures

Making composite with polymers Chemical Vapor deposition of graphene Proposed Incredible Uses for Graphene

Scientists at Rice say graphene could Water, water everywhere and EVERY drop drinkable. MIT potentially clump together radioactive mind s have a plan for a graphene filter covered in tiny waste, making disposal is a breeze. holes just big enough to let water through and small enough to keep salt out, making salt water safe for consumption.

Touchscreens that use graphene as their conductor could be slapped onto plastic rather than glass. That would mean super thin, unbreakable touchscreens and a replacement for ITO Just a single sheet of graphene could produce headphones that have a frequency response comparable to a pair of Sennheisers, as some scientists at UC Berkeley recently showed.

Graphene could pave the way for bionic devices in living tissues that could be connected directly to your neurons. So people with spinal injuries, for example, could re-learn how to use their limbs. Graphite Intercalation Compounds

One of the best studied graphite intercalation compounds, KC8, is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite increasing the interlayer distance from 335 to 540 nm and the material changes color from black to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite.KC 8 is a superconductor with a very low critical temperature Tc = 0.14 K. The gold-colored material KC 8 is one of the strongest reducing agents known. It has also been used as a catalyst in polymerizations and as a coupling reagent for aryl halides to biphenyls .

N N N 4KC8, THF Si Si SiCl4 N RT N N Carbon Black

Quantity wise the maximum produced carbon allotrope

Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of activated carbon

Total production was around 8,100,000 metric tons in 2006. The most common use (70%) of carbon black is as a pigment and reinforcing phase in automobile tires . Carbon black also helps conduct heat away from the tread and belt area of the tire, reducing thermal damage and increasing tire life. Carbon black particles are also employed in some radar absorbent materials and in photocopier and laser printer toner, and other inks and paints.

About 20% of world production goes into belts, hoses, and other non-tire rubber goods. Allotropes of carbon:

a) Diamond, b) Graphite, c) Lonsdaleite (meteoric graphite)

d) C 60 (Buckminster fullerene or buckyball), e) C 540 , f) C 70 , g) Amorphous carbon, and h) single-walled carbon nanotube i. Graphene j. Linear Acetylenic carbon K. glassy carbon L. Carbon nanobud M. Carbon nanofoam

Etc…………