MOSCOW, May 27. /TASS/. A group of Russian and Italian scientists have experimentally confirmed a model to detect electron delocalization in molecules and crystals, the Moscow Institute of Physics and Technology (MIPT) said on Friday.
Physicists from the Institute of Molecular Science and Technologies (ISTM-CNR, Italy), MIPT, and the University of Milan have also illustrated examples on how the same approach have been used to obtain precious insights into the chemical bonding of a wide variety of systems, from metallorganic compounds to systems of biological relevance.
As electrons are quantum objects, they cannot be clearly identified (or, to use the scientific term, localized) in a particular place. This means that the behavior of electrons cannot be described using equations that work with regular, non-quantum objects: instead of an electron as a ball within a molecule, scientists have to examine a blurred cloud. Developing a mathematical model to determine the distribution of electrons relatively quickly and accurately is one of the most significant challenges of modern science.
"The main novelty introduced by our study is the possibility of detecting electron delocalization directly from experimental data. Electron delocalization, which is a cornerstone paradigm of chemistry (fundamental, for example, for understanding aromaticity), could so far be estimated only through approaches relying on quantities not obtainable from experimental measurements, e.g. the so-called ‘delocalization index. Our results may therefore pave the way for a novel way of looking at this important phenomenon," said Gabriele Saleh, one of the co-authors of the study.
The mathematical model proposed in 1998 by the Canadian expert in quantum chemistry Richard Bader and the Italian researcher Carlo Gatti see electron distribution in a crystal as the sum of contributions of so-called Source Functions. From this point of view, a molecule (or crystal) is seen as a set of individual elements, each of which contributes to the final distribution. This approach, as shown by subsequent studies, provides an insightful view of hydrogen bonds, metal-ligand bonds, and other types of chemical interactions.
From theory to practice
In 2016, Carlo Gatti, Gabriele Saleh (researcher at MIPT Laboratory of Computer Design of Materials) and Leonardo Lo Presti of the University of Milan demonstrated yet another use of the Bader-Gatti approach for studying chemical bonding directly from experimental results. In these experiments X-ray beam is directed onto a sample and once it passes through it, it is diffracted. By looking at how this diffraction occurs and in which direction particles are deflected, physicists are able to make conclusions about the distribution of electrons within a crystal under study - this distribution is described using the concept of electron density. The researchers note that the results allow the Bader-Gatti model to be used to describe the subtle effects associated with electron delocalization in organic molecular crystals.
The modelling of molecules and crystals is important both from a theoretical and from a practical point of view. Data on electron density is also needed to help discover new drugs (to identify exactly which molecules can reach a target protein and react with it), and to calculate the characteristics of materials formed by various molecules. Among the prospects for further research, the main priority will be to study the density of not only electrons, but also their spins - characteristics which determine the magnetic properties of a material. Organic magnets (which can be developed based on the results of this research) have more flexible properties and are cheaper to manufacture than metal-based magnets.