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Caesium in high oxidation states and as a p-block element

Abstract

The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry, rooted in the atomic shell structure. Within compounds, Group I elements, for example, invariably assume the +1 oxidation state, and their chemical properties differ completely from those of the p-block elements. These general rules govern our understanding of chemical structures and reactions. Here, first-principles calculations show that, under pressure, caesium atoms can share their 5p electrons to become formally oxidized beyond the +1 state. In the presence of fluorine and under pressure, the formation of CsFn (n > 1) compounds containing neutral or ionic molecules is predicted. Their geometry and bonding resemble that of isoelectronic XeFn molecules, showing a caesium atom that behaves chemically like a p-block element under these conditions. The calculated stability of the CsFn compounds shows that the inner-shell electrons can become the main components of chemical bonds.

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Figure 1: Stability of CsFn compounds under pressure.
Figure 2: Crystal structures of CsFn compounds, and selected interatomic distances as functions of pressure.
Figure 3: Electronic structures and the nature of Cs–F bonds.
Figure 4: Mechanism of pressure-driven high oxidation states.

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Acknowledgements

The author thanks R. Hoffmann at Cornell University and R. Seshadri at University of California Santa Barbara for inspiring discussions and constructive suggestions. This work was supported by the Materials Research Science and Engineering Center programme (National Science Foundation (NSF)-Division of Materials Research (DMR)1121053) and the Conversion of Energy Through Molecular Platforms-The Integrative Graduate Education and Research Traineeship programme (NSF-Division of Graduate Education (DGE)0801627). Calculations were performed on resources at the Center for Scientific Computing, supported by the California NanoSystems Institute, Materials Research Lab. and NSF (Division of Computer and Network Systems (CNS)-0960316), on NSF-funded Extreme Science and Engineering Discovery Environment resources (Teragrid (TG)-DMR130005) and on Beijing Computational Science Research Center computing resources.

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Correspondence to Mao-sheng Miao.

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Miao, Ms. Caesium in high oxidation states and as a p-block element. Nature Chem 5, 846–852 (2013). https://doi.org/10.1038/nchem.1754

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