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How Far Can One Push the Noble Gases Towards Bonding?: A Personal Account

Department of Chemistry and Centre for Theoretical Studies Indian Institute of Technology Kharagpur, Kharagpur 721302, India
Institute of Advanced Synthesis, School of Chemistry and Molecular Engineering, Jiangsu National Synergetic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 211816, China
Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados, Unidad Mérida. Km 6 Antigua Carretera a Progreso. Apdo. Postal 73, Cordemex, Mérida 97310, Yuc., Mexico
Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India
Authors to whom correspondence should be addressed.
Molecules 2019, 24(16), 2933;
Received: 13 July 2019 / Revised: 29 July 2019 / Accepted: 30 July 2019 / Published: 13 August 2019
(This article belongs to the Special Issue The Molecular Electron Density Theory in Organic Chemistry)
PDF [3835 KB, uploaded 13 August 2019]


Noble gases (Ngs) are the least reactive elements in the periodic table towards chemical bond formation when compared with other elements because of their completely filled valence electronic configuration. Very often, extreme conditions like low temperatures, high pressures and very reactive reagents are required for them to form meaningful chemical bonds with other elements. In this personal account, we summarize our works to date on Ng complexes where we attempted to theoretically predict viable Ng complexes having strong bonding to synthesize them under close to ambient conditions. Our works cover three different types of Ng complexes, viz., non-insertion of NgXY type, insertion of XNgY type and Ng encapsulated cage complexes where X and Y can represent any atom or group of atoms. While the first category of Ng complexes can be thermochemically stable at a certain temperature depending on the strength of the Ng-X bond, the latter two categories are kinetically stable, and therefore, their viability and the corresponding conditions depend on the size of the activation barrier associated with the release of Ng atom(s). Our major focus was devoted to understand the bonding situation in these complexes by employing the available state-of-the-art theoretic tools like natural bond orbital, electron density, and energy decomposition analyses in combination with the natural orbital for chemical valence theory. Intriguingly, these three types of complexes represent three different types of bonding scenarios. In NgXY, the strength of the donor-acceptor Ng→XY interaction depends on the polarizing power of binding the X center to draw the rather rigid electron density of Ng towards itself, and sometimes involvement of such orbitals becomes large enough, particularly for heavier Ng elements, to consider them as covalent bonds. On the other hand, in most of the XNgY cases, Ng forms an electron-shared covalent bond with X while interacting electrostatically with Y representing itself as [XNg]+Y. Nevertheless, in some of the rare cases like NCNgNSi, both the C-Ng and Ng-N bonds can be represented as electron-shared covalent bonds. On the other hand, a cage host is an excellent moiety to examine the limits that can be pushed to attain bonding between two Ng atoms (even for He) at high pressure. The confinement effect by a small cage-like B12N12 can even induce some covalent interaction within two He atoms in the He2@B12N12 complex. View Full-Text
Keywords: noble gas; electron density; bonding; electron localization function; energy decomposition analysis noble gas; electron density; bonding; electron localization function; energy decomposition analysis

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Saha, R.; Jana, G.; Pan, S.; Merino, G.; Chattaraj, P.K. How Far Can One Push the Noble Gases Towards Bonding?: A Personal Account. Molecules 2019, 24, 2933.

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