ESRF Highlights 2023

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PRINCIPAL PUBLICATION AND AUTHORS

Unraveling the Bonding Complexity of Polyhalogen Anions: High-Pressure Synthesis of Unpredicted Sodium Chlorides Na2Cl3 and Na4Cl5 and Bromide Na4Br5, Y. Yin (a,b), AL. Aslandukova (c), N. Jena (d), F. Trybel (d), I.A. Abrikosov (d), B. Winkler (e), S. Khandarkhaeva (c), T. Fedotenko (f), E. Bykova (c,g), D. Laniel (h), M. Bykov (i), A.N. Aslandukov (a,c), F.I. Akbar (a,c), K. Glazyrin (f), G. Garbarino (j), C. Giacobbe (j), E.L. Bright (j), Z. Jia (b), L. Dubrovinsky (c), N. Dubrovinskaia (a,d), J. Am. Chem. Soc. Au 3, 1634-1641 (2023); https:/doi.org/10.1021/jacsau.3c00090 (a) Material Physics and Technology at Extreme Conditions, Laboratory of Crystallography, University of Bayreuth, Bayreuth (Germany) (b) State Key Laboratory of Crystal Materials, Shandong University, Jinan (China) (c) Bayerisches Geoinstitut, University of Bayreuth, Bayreuth (Germany) (d) Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping (Sweden) (e) Institute für Geowissenschaften, Frankfurt University, Frankfurt am Main (Germany) (f) Photon Science, Deutsches Elektronen-Synchrotron, Hamburg (Germany) (g) Earth and Planets Laboratory, Carnegie Institution for Science, Washington DC (USA) (h) Centre for Science at Extreme Conditions and School of Physics and Astronomy, University of Edinburgh, Edinburgh (UK) (i) Institute of Inorganic Chemistry, University of Cologne, Cologne (Germany) (j) ESRF

the chemical composition of the products of reactions in a laser-heated DAC and has become the ultimate method of high-pressure chemical crystallography.

Single-crystal XRD analysis using the DAFi program revealed three novel sodium chlorine and sodium bromine compounds that have never been predicted from ab- initio calculations: the isostructural hP18-Na4Cl5 and hP18-Na4Br5 (Pearson symbol hP18; space group P63/mcm, #193; Figure 94a) and tP10-Na2Cl3 (space group P4/mbm, #127; Figure 94b). Their chemical formulas resulted from a structure solution and refinement. The formation of a series of cP8-AX3 isostructural halides (space group Pm 3n, #223), NaCl3, KCl3, KBr3, and NaBr3-x, and a trigonal potassium chloride (hP24-KCl3), were also observed in the corresponding A-X systems.

Synchrotron single-crystal XRD at beamlines ID11 and ID27 beamlines provided the first accurate structural data for the symmetric trichloride Cl3- anion in hP24-KCl3 and revealed the existence of two different types of infinite linear polyhalogen chains, [Cl]∞

n- and [Br]∞ n-,

in the structures of cP8-AX3 compounds and in hP18- Na4Cl5 and hP18-Na4Br5. Crystal chemical analysis and theoretical calculations demonstrate that the polyhalogen chains possess conjugated σ-systems but with obvious differences, eg., in the electron localisation function of polyanions in cP8-NaX3 trichlorides (Figure 95a) and hP18-Na4X5 (Figure 95b).

This study demonstrates that the chemistry of polyhalogen anions in alkali halides at high pressures is significantly more complex than predicted by density functional theory calculations and/or revealed by existing experimental data. These results give a new insight into the chemistry of polyhalides.

Fig. 95: a) Electron localisation function calculated in (001) plane for cP8-NaCl3 and (b) in (110) plane for hP18-Na4Cl5. The isosurfaces value is set as 0.3.