IFIMAC+ICMM Joint Seminar Series focuses on cutting-edge research on condensed matter physics, bringing speakers from all over the world to our Cantoblanco Campus. All talks are streamed online. Some of them will be celebrated on campus and onsite participation will also be possible. You need to subscribe to our mailing list at the link provided below to get the links to the seminar room. https://listas-correo.uam.es/sympa/subscribe/seminarios-ifimac-icmm-l
Imaging the anisotropic charge distribution within a single atom with Scanning Probe Microscopy
Bruno de la Torre, Regional Centre of Advanced Technologies and Materials, Palacký University, Olomouc, CZ
February 10th, 2022, 12:00 CET
An anisotropic charge distribution on individual atoms may strongly affect the material and structural properties of systems. An example of this is the halogen bond which steer the atomic arrangement of molecular structures possessing two adjacent halogens or pair of halogen atoms and electron donor motifs. The formation of a covalent bond between certain halogen atoms (chlorine, bromine, and iodine) and a more electronegative atom (such as carbon) gives rise to a so-called σ-hole that form intermolecular bonds stabilizing the structure. The concept of halogen bonding has been generalized expanding to the halogen (group 17), chalcogen (group 16), pnicogen (group 15), tetrel (group 14), and aerogen bonding (group 18).
The characteristic shape of the σ-hole is formed by a positively charged crown surrounded by a belt of negative electron density. This inhomogeneous charge distribution leads to the formation of a halogen bond, which plays a key role in, among other things, supramolecular chemistry, including molecular crystal engineering, and in biological systems. However, the spatial resolution of such anisotropic charge distributions on an atom represents a long-standing experimental challenge. In particular, the existence of the σ-hole on halogen atoms has been demonstrated only indirectly through the determination of the crystal structures of organic molecules containing halogens or with theoretical calculations, consequently calling for its direct experimental visualization. I will show that Kelvin probe force microscopy with a properly functionalized probe can image the anisotropic charge of the σ-hole. This opens a new way to characterize biological and chemical systems in which anisotropic atomic charges play a decisive role.
