Scientists have captured video of a pair of rhenium atoms breaking apart and bonding again in a carbon nanotube. The study, published in Science Advances on January 17, used a beam of electrons as both a tool for imaging and as a source of energy for the atoms’ movements.
The atoms’ dance plays out at nano-scale. Their bonds are only 0.1 to 0.3 nanometers long, so the research team used transmission electron microscopy (TEM) to observe the atoms caught in a carbon nanotube. TEM requires shooting a beam of electrons into the sample at a low voltage to avoid damage, reports Emily Conover at Science News. The unique setup also provides sharper resolution of the tiny subjects.
Molecules, like the bonded pair of rhenium atoms called dirhenium, need an input of energy in order to modify or break their bonds. The electron beam was perfect for the task. The microscope captured a series of images showing the atoms moving together and apart as they moved along the nanotube. In one unusual moment, the atoms were split apart, and one settled in a different carbon nook than its partner before returning and forming a bond again.
“This is direct evidence, you can see how this bond breaks between the two atoms and how it forms,” lead author and University of Nottingham chemist Andrei Khlobystov says to Chemistry World’s Andy Extance. The video revealed a never-before-observed bonding state just before the bond was broken. “This is, I think, extremely important.”
Rhenium is a rare transition metal, found at a concentration of about 0.001 parts per million in minerals around the world, particularly in Chile and the United States. As a transition metal, rhenium can be creative with its bonds. Atoms form chemical bonds by either giving away or sharing the negatively charged electrons that surround their positively charged cores. Most atoms can only form bonds with the electrons on their outermost shells, but transition metals can use the electrons from two outer layers.
The researchers found that a molecule of dirhenium spends most of its time with a quadruple bond, sharing four electrons between the two atoms. The electron beam also pushed the molecule into triple, double, and single-bonded states, which the researchers estimate from the distance they observe between the atoms.
Ulm University physicist Ute Kaiser, a developer of the microscopy filming technique, tells Science News that the direct observation of changing chemical bonds “was not done before” this study. Kaiser and his colleagues chose rhenium because each atom is relatively large, compared more familiar atoms like carbon and oxygen that are less than one tenth of its atomic weight. But they hope to continue developing the technology to study those smaller elements, perhaps as a new way to study what’s happening in complex chemical reactions directly.
“For me, the most exciting aspect of the walk is how the detailed electronic structure changes,” says Frank Wagner, a chemical metals specialist at the Max Planck Institute for Chemical Physics of Solids, to Chemistry World. But he adds that the study may be relying on a “simplified picture,” and is waiting to see further calculations.