Fullerene chemistry
According to Euler's theorem these 12 pentagons are required for closure of the carbon network consisting of n hexagons and C60 is the first stable fullerene because it is the smallest possible to obey this rule.
Because of the molecule's spherical shape the carbon atoms are highly pyramidalized, which has far-reaching consequences for reactivity.
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.
The fullerene is able to acquire the missing electrons by reaction with potassium to form first the K6C6−60 salt and then the K12C12−60 In this compound the bond length alternation observed in the parent molecule has vanished.
In conformity with IUPAC rules, the terms methanofullerene are used to indicate the ring-closed (cyclopropane) fullerene derivatives, and fulleroid to ring-open (methanoannulene) structures.
For example, the reaction of C60 with methylmagnesium chloride stops quantitatively at the penta-adduct with the methyl groups centered around a cyclopentadienyl anion which is subsequently protonated.
[10] The [6,6] bonds of fullerenes react as dienes or dienophiles in cycloadditions for instance Diels-Alder reactions.
At the final reaction stage this causes collapse of cage structure with formation of polycyclic aromatic hydrocarbons.
[15][16] Another method is reaction in diluted sodium hydroxide catalysed by TBAH adding 24 to 26 hydroxyl groups.
According to in silico predictions the as yet elusive C60F60 may have some of the fluorine atoms in endo positions (pointing inwards) and may resemble a tube more than it does a sphere.
The unpaired electron does not delocalize over the entire sphere but takes up positions in the vicinity of the tBu substituent.
All reported derivatives are η2 complexe in which the metal coordinates at a six–six ring fusion with formal double bond.
[30][31] Based on spectroscopy, substitutions have been reported with boron (borafullerenes),[32][33] nitrogen (azafullerenes),[34][35] oxygen,[36] arsenic, germanium,[37] phosphorus,[38] silicon,[39][40] iron, copper, nickel, rhodium[40][41] and iridium.
[14] The C60 fullerene dimerizes in a formal [2+2] cycloaddition to a C120 bucky dumbbell in the solid state by mechanochemistry (high-speed vibration milling) with potassium cyanide as a catalyst.
[50][51] In the final step a large polycyclic aromatic hydrocarbon consisting of 13 hexagons and three pentagons was submitted to flash vacuum pyrolysis at 1100 °C and 0.01 Torr.
Continuous high-resolution transmission electron microscopic video imaging of the electron-beam-induced bottom-up synthesis of fullerene C60 through cyclodehydrogenation of C60H30 was reported in 2021.
[52] A similar exercise aimed at construction of a C78 cage in 2008 (but leaving out the precursor's halogens) did not result in a sufficient yield but at least the introduction of Stone Wales defects could be ruled out.
A practical laboratory-scale method for purification of soot enriched in C60 and C70 starts with extraction in toluene followed by filtration with a paper filter.
The solvent is evaporated and the residue (the toluene-soluble soot fraction) redissolved in toluene and subjected to column chromatography.
It is assumed that this oxidation creates oxygen containing groups (hydroxyl, carbonyl, carboxyl) on the nanotube surface which electrostatically stabilize them in water and which can later be utilized in chemical functionalization.
One report [56] reveals that the oxygen containing groups in actuality combine with carbon contaminations absorbed to the nanotube wall that can be removed by a simple base wash. Cleaned nanotubes are reported to have reduced D/G ratio indicative of less functionalization, and the absence of oxygen is also apparent from IR spectroscopy and X-ray photoelectron spectroscopy.
DBU as it turns out only reacts to C70 fullerenes and higher which reaction products separate out and can be removed by filtration.
A separation method for both fullerenes based on this principle is made possible by anchoring cyclodextrin to colloidal gold particles through a sulfur-sulfur bridge.
[58] The Au/CD compound is very stable and soluble in water and selectively extracts C60 from the insoluble mixture after refluxing for several days.
