Chemists have created a ring-shaped form of carbon | Science News for Students

Chemists have created a ring-shaped form of carbon

Called cyclocarbon, this molecule is the latest lab-made form of the universal element
Sep 9, 2019 — 6:45 am EST
an illustration of a new 18-atom carbon ring

Chemists created a new form of carbon called cyclocarbon. The 18-atom ring is illustrated here using data from an atomic force microscope. Bonds between the atoms are alternately longer and shorter, giving the ring nine sides.

IBM Research

A highly anticipated new form of carbon has finally arrived on the scene.

Called cyclocarbon, this molecule consists of a ring of 18 carbon atoms. Scientists described it online August 15 in Science. It offers a new face to one of chemistry’s most celebrated elements.

“It’s not every day that you make a new form of carbon,” says chemist Rik Tykwinski. He works in Canada at the University of Alberta in Edmonton. Chemists had been trying to create cyclocarbon for a long time. So long that Tykwinski — who wasn’t involved with the new research — had placed a bet about whether it was even possible. He won, he says.

Cyclocarbon joins other molecular forms of the adaptable element, from diamond and graphite to the thin sheets called graphene. There are also tiny spheres known as buckyballs and nano-scale cylinders called carbon nanotubes.

Chemists thought it should be possible to create ring-shaped carbon molecules. But until now, nobody knew what their properties would be, notes physicist Katharina Kaiser. She’s at IBM Research in Zurich, Switzerland.It’s really amazing that we found it,” she says, “and it’s absolutely great that we could characterize it.”

Kaiser’s team started with molecules of cyclocarbon oxide. These are made of carbon and other atoms. They included groups of carbon monoxide (pairs of carbon and oxygen atoms). Removing the carbon monoxide was a necessary step to create the new ring form of carbon. But that was no easy task. Carbon monoxide helped to stabilize the starting molecule. The researchers managed to pluck off the carbon monoxide groups by zapping the molecule with electricity. They used a specialized tool called an atomic force microscope.

Once the researchers had a bare ring of carbon, they wanted to capture an image of its structure. Again, they used the atomic force microscope. Cyclocarbon reacts easily with other substances — but not table salt. So the team created the new carbon molecule on a salty surface.

Previous research had found hints of cyclocarbon molecules in a gas. But it wasn’t possible to make an image of those molecules. So scientists couldn’t identify the bonds holding the molecule together. Scientists wanted to know if all the bonds were the same length.

The new study resolved that question. It showed that the carbon atoms are held together by alternating long and short bonds.

an illustration of the cyclocarbon structure
Cyclocarbon has 18 carbon atoms arranged in a ring, as seen in this simulation. There’s an alternating pattern of long and short bonds between the atoms.
IBM Research

That should now help scientists refine the computer calculations used to predict the structures of unknown molecules. “There’s still a big question whether many of these … calculations give the right answer,” says Yves Rubin. “So it’s very important to confirm by experiment.” Rubin is a chemist at the University of California, Los Angeles, who also was not involved with the study.

Previous work on new forms of carbon caused great excitement among scientists. The discovery in the 1980s of buckyballs (and the family of molecules that includes them, called fullerenes) won a Nobel Prize. Likewise, the 2004 discovery of graphene won a Nobel. Investigations into its many potential uses in electronics and elsewhere have continued.

But because cyclocarbon isn’t stable, it can’t be bottled up for further study. So, for now, it’s not clear how wide-ranging this new molecule’s impact will be.

Power Words

(more about Power Words)

atom     (adj. atomic) The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

bond     (in chemistry) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It’s formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation.

carbon     The chemical element having the atomic number 6. It is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules.

carbon monoxide     A toxic gas whose molecules include one carbon atom and one oxygen atom. (The “mono” in “monoxide” is a prefix from Greek that means “one”.)

carbon nanotube     A nanoscale, tube-shaped material, made from carbon that conducts heat and electricity well.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. People who work in this field are known as chemists.

diamond     One of the hardest known substances and rarest gems on Earth. Diamonds form deep within the planet when carbon is compressed under incredibly strong pressure.

electricity     A flow of charge, usually from the movement of negatively charged particles, called electrons.

electronics     Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.

element     A building block of some larger structure. (in chemistry) Each of more than one hundred substances for which the smallest unit of each is a single atom. Examples include hydrogen, oxygen, carbon, lithium and uranium.

fullerenes     Molecules of carbon that resemble tiny, soccer ball–like cages when the chemical bonds between all of the carbon atoms are drawn. Fullerenes, which chemists first created in 1985, are nicknamed “buckyballs” after Buckminster Fuller, the famous architect and engineer who designed dome-shaped structures that resemble fullerene molecules.

graphene     A superthin, superstrong material made from a single-atom-thick layer of carbon atoms that are linked together.

graphite     Like diamond, graphite (the substance found in pencil lead) is a form of pure carbon. Unlike diamond, graphite is very soft. The main difference between these two forms of carbon is the number and type of chemical bonds between carbon atoms in each substance.

microscope     An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

nano     A prefix indicating a billionth. In the metric system of measurements, it’s often used as an abbreviation to refer to objects that are a billionth of a meter long or in diameter.

Nobel prize     A prestigious award named after Alfred Nobel. Best known as the inventor of dynamite, Nobel was a wealthy man when he died on December 10, 1896. In his will, Nobel left much of his fortune to create prizes to those who have done their best for humanity in the fields of physics, chemistry, physiology or medicine, literature and peace. Winners receive a medal and large cash award.

online     (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.

oxide     A compound made by combining one or more elements with oxygen. Rust is an oxide; so is water.

oxygen     A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

physicist     A scientist who studies the nature and properties of matter and energy.

salt     A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine.

Citation

Journal:​ K. Kaiser et al. An sp-hybridized molecular carbon allotrope, cyclo[18]carbon. Science. Published online August 15, 2019. doi: 10.1126/science.aay1914.