Chemistry under high pressure

Abstract

Thanks to the development of experimental high-pressure techniques and methods for crystal-structure prediction based on quantum mechanics, in the past decade, numerous new compounds, mostly binary, with atypical compositions have been predicted, and some have been synthesized. Differing from conventional solid-state materials, many of these new compounds are comprised of various homonuclear chemical species, such as dimers, trimers, pentagonal and heptagonal rings, polymeric chains, atomic layers and 3D networks. Strikingly, it has been shown that pressure can alter the chemistry of an element by activating its (semi)core electrons, unoccupied orbitals and even the non-atom-centred quantum orbitals located on the interstitial sites, leading to many new surprising phenomena. This Review provides a summary of atypical compounds that result from the effects of high pressure on either the chemical bonds or the local orbitals. We describe various unusual chemical species and motifs, show how the chemical properties of the elements are altered under pressure and illustrate how compound formation is favoured even in situations in which chemical bonds are not formed. An extraordinary new picture of chemistry emerges as we piece together these unexpected high-pressure phenomena. In marked contrast to the previously held beliefs regarding the behaviour of solids under pressure, we are learning that the quantum-mechanical features of electrons, such as those that lead to the formation of directional bonds, inhomogeneous distributions of electrons and atoms, as well as variations in symmetry, might be magnified under pressure. We discuss the influence of these phenomena on future studies that will probe chemistry at higher pressures and explore more complex chemical compositions than those that have been studied to date.

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Fig. 1: Selected homonuclear species present in atypical high-pressure compounds.
Fig. 2: Predicted structural evolution of compounds formed via the involvement of non-valence electrons and orbitals under pressure.
Fig. 3: Chemistry of core electrons.
Fig. 4: Chemistry of non-valence orbitals.
Fig. 5: Quasiatoms and their chemistry.
Fig. 6: Chemistry without chemical bonds and the mechanism of He insertion in ionic compounds.

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Acknowledgements

M.M. and Y.S. acknowledge the support of NSF CAREER award 1848141 and computational resources provided by XSEDE (TG-DMR130005). M.M. also acknowledges the support of ACS PRF 59249-UNI6. E.Z. acknowledges the support of NSF (DMR-1827815) and DOE (DE-SC0020340). H.L. acknowledges financial support from NSAF U1930402 and computational resources from the Beijing Computational Science Research Center.

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M.M. conceived the synopsis of the article, proposed the conceptual framework and wrote the first draft. M.M. and E.Z. made major revisions to the article. E.Z. wrote Box 1 and made major contributions to the section on hydrides. Y.S. made Table 1, Fig. 1, contributed to the literature search and helped with the other figures. H.L. supported and discussed the research and writing.

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Correspondence to Maosheng Miao.

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Miao, M., Sun, Y., Zurek, E. et al. Chemistry under high pressure. Nat Rev Chem 4, 508–527 (2020). https://doi.org/10.1038/s41570-020-0213-0

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