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Posted: May 29, 2015

Researchers use AFM to determine nature of halogen bonds

(Nanowerk News) An international research team from Iran, Japan, and Switzerland studied the nature of halogen bond between fluorine atoms.
Results of the research (ACS Nano, "Extended Halogen Bonding between Fully Fluorinated Aromatic Molecules") have applications in pharmaceutical and nanotechnology researches.
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The team studied atomic-scale in-plane FF contacts with high-resolution force microscopy. Our ab initio calculations show that the attractive dispersion forces can overcome the electrostatic repulsion between the fluorine atoms, while the anisotropic distribution of the negative electrostatic potential leads the directional bond and even changes the gap. (© ACS)
In the past decades, the importance of halogen bond has been discovered and studied in biological or non-biological systems more than any other time. Halogen bonds are very important in the production and formulation of drugs to increase their effectiveness, and also in the designing of layer structures, liquid crystals and gels.
Dr. Ali Sadeqi, one of the Iranian researchers, explained that halogen bonds are very weak in fluorine and they do not usually occur. He continued, It is not easy to study the nature of the bond. In this research, the creation of halogen bond between fluorine atoms were made possible by creating a single layer on the surface of aromatic molecules, in which all hydrogen atoms are replaced with fluorine. Therefore, a new type of two-dimensional molecular crystal was introduced due to the halogen bonds between the fluorine atoms.
In this experimental and theoretical research, the geometric structure of the molecular layer was detected by atomic force microscope with very high resolution. Then, the nature of intra-molecular bond was studied by using accurate calculations based on quantum mechanics. The majority of halogen bonds that we know are based on halogen atom due to the presence of a very small area with positive electrical potential. However, there is no such area in fluorine atom, and a special type of halogen bond is created. According to the studies, Van der Waals Force plays an important role in the creation of the bond. In addition, the final bond has direction due to the asymmetric distribution of electrical potential around fluorine atoms, he added.
Source: INIC
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