Enrico Uva

Although we often see isolated water molecules in textbooks, in reality they rarely exist as hermits. They are not only small but hydrogen-bonded to one another, as if an oxygen atom of one water particle coveted the hydrogen atoms of neighboring molecules. But this summer(2011), Japanese researchers from Kyoto University published that they had performed the feat of imprisoning one single molecule of water. They synthesized an open-cage C₆₀ derivative, one whose opening could be made bigger at 120 ^oC, and then at high pressure , a single H₂O molecule was admitted. The cage was closed, and H₂O was trapped. Single-crystal x-ray analysis, along with its physical and spectroscopic properties confirmed the structure of H₂O@C₆₀.

The 1996 Nobel Prize in Chemistry for the synthesis of fullerenes certainly did not slow the pace of fullerene research, especially in Japan where there are thousands of patents related to its use. So it's not a coincidence that they used a fullerene to trap water's fundamental unit.

Buckminsterfullerene is the name given to the simplest of the fullerenes. The C₆₀ molecule is shaped like a soccer ball with pentagonal and hexagonal faces. Each of the 60 carbon atoms is a vertex on both a pentagon and a hexagon, but none of the pentagons are adjacent to each other, so there are 60/5 = 12 pentagons.

Each pentagon is attached to 5 hexagons but each hexagon is shared by 3 pentagons, so there are 12(5)/3 = 20 hexagons.

The structure follows Euler's polyhedron formula, |V|-|E|+|F| = 2, (where |V|, |E|, |F| indicate the number of vertices, edges, and faces). If we apply the formula to C60 :

60 – E + (20 + 12) = 2

E = 90, so the molecule has ‘90 edges’.

Only after it was synthesized (in 1985) was it realized that C₆₀ is found in candle soot.

Fullerenes such as C₆₀ are formed when vaporized carbon condenses in a noble gas atmosphere. The gaseous carbon can be obtained by directing an intense pulse of laser light at carbon’s surface. The released carbon atoms were mixed with a stream of helium gas and combine to form clusters of up to hundreds of atoms. It took about five years after the initial discovery to make appreciable quantities of the compound, and it became apparent that this discovery would father a fair amount of new chemistry. Before trapping water in a fullerene, scientists were also successful in capturing single ions such as lanthanum(La⁺) and cesium(Cs⁺) in C₆₀. In fact these experiments had helped confirm the structure of buckminsterfullerene when it was still in the hypothetical stage.

References

Science Magazine29 July 2011

What's Fullerene?

http://nobelprize.org/nobel_prizes/chemistry/laureates/1996/press.html

http://www.vc60.com/english/fullerene/index.html

http://sciam.com/askexpert_question.cfm

http://en.wikipedia.org/wiki/Buckminsterfullerene

Hugh Aldersey-Williams. The Most Beautiful Molecule: An Adventure in Chemistry, Aurum Press. London. 1995.