filming chemical bond dynamics

Filming Chemical Bond Dynamics at Atomic Level Made Possible by Scientists

Scientists have been trying to understand how and why they bond to each other ever since it was proposed that atoms are building blocks of the world. Everything is controlled by the way atoms bond and the way bonds break, be it a whole organism, a block of material, or a molecule.

The length of a chemical bond is a million times smaller than the width of a human hair, between 0.1 — 0.3 nm. This makes the direct imaging of the chemical bonds difficult. Filming the bonding and breaking of chemical bonds in real-time with spatiotemporal continuity is one of the greatest challenges in science even though atomic positions and bond lengths can be directly measured through advanced microscopic methods like atomic force microscopy (AFM) or scanning tunneling microscopy (STM).

A research team from the Germany and UK led by Professor Andrei Khlobystov in the School of Chemistry at the University of Nottingham and Professor Ute Kaiser, head of the Electron Microscopy of Materials Science in the University of Ulm have published ‘Imaging an unsupported metal-metal bond in dirhenium molecules at the atomic scale’ in Science Advances.


Miniature test tubes for atoms

This group of scientists was among the first to film chemical reactions at the single-molecule level using transmission electron microscopy (TEM). They also filmed the dynamics of metal atoms in nanocatalysts using carbon nanotubes. Nanotubes are miniature test tubes for atoms that are atomically thin hollow cylinders of carbon with diameters at the molecular scale (1-2 nm).

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Nanotubes are used to catch molecules or atoms and to position them wherever the scientists want. Here scientists formed Re2 by trapping a pair of rhenium (Re) atoms. Each metal atom in Re2 could be identified as a dark spot as it has a high atomic number, which makes it possible to see in TEM compared to lighter elements.

They were able to see the atomic-scale dynamics of Re2 adsorbed on the graphitic lattice of the nanotube as they imaged the diatomic molecules by the state of the art chromatic and spherical aberration-corrected SALVE TEM.

A two-in-one trick

The team uses electron beam for two purposes; for the activation of chemical reactions with the help of energy transferred from fast electrons of the electron beam to the atoms and for the precise imaging of atomic positions. This trick allowed scientists to record chemical reactions in the past, and now they are using the trick to film the bonding between two atoms in Re2. In the recorded movie, the two atoms were moving in pairs, clearly indicating the bond between them. The bond length between the atoms in Re2 changed while moving down the nanotube, which indicates that the bond strength between atoms varies depending on the environment around the atoms.

Breaking the bond

The atoms of Re2 started vibrating after a period of time, distorting their circular shapes into ellipses, eventually stretching the bond. Once the bond length exceeded the sum of atomic radii,  the bond broke, and the vibration stopped indicating that the atoms are independent of each other. After some time, the atoms bonded again forming Re2 molecule.

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For understanding electronic, catalytic, or magnetic properties of materials, bonds between metal atoms are crucial. The possibility of forming bonds of different order, from single to quintuple bonds makes it challenging in the case of transition metals. The two rhenium atoms in this TEM experiment were observed to form a quadruple bond providing new fundamental insights into transition metal chemistry.

Electron microscope: A new analytical tool for chemists

It is for the first time that the formation, breaking, and evolution of chemical bonds are being filmed at the atomic scale. With the advent of cryogenic TEM, which received the Nobel Prize in 2017, electron microscopy is becoming an analytical tool for determining structures of molecules. The scientists hope that electron microscopy would one day become the common method for understanding chemical reactions.


Editor’s Note; filming chemical bond dynamics, Re2 molecule in nanotube, bond length varies. recording of chemical bonding.

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