Unraveling the Bonding Complexity of Polyhalogen Anions: High-Pressure Synthesis of Unpredicted Sodium Chlorides Na 2 Cl 3 and Na 4 Cl 5 and Bromide Na 4 Br 5 .

The field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides), is rapidly evolving. Here, we present the synthesis of three sodium halides with unpredicted chemical compositions and structures ( tP 10-Na ₂ Cl ₃ , hP 18-Na ₄ Cl ₅ , and hP 18-Na ₄ Br ₅ ), a series of isostructural cubic cP 8-AX ₃ halides (NaCl ₃ , KCl ₃ , NaBr ₃ , and KBr ₃ ), and a trigonal potassium chloride ( hP 24-KCl ₃ ). The high-pressure syntheses were realized at 41-80 GPa in diamond anvil cells laser-heated at about 2000 K. Single-crystal synchrotron X-ray diffraction (XRD) provided the first accurate structural data for the symmetric trichloride Cl ₃ ^- anion in hP 24-KCl ₃ and revealed the existence of two different types of infinite linear polyhalogen chains, [Cl] _∞ ^{n -} and [Br] _∞ ^{n -} , in the structures of cP 8-AX ₃ compounds and in hP 18-Na ₄ Cl ₅ and hP 18-Na ₄ Br ₅ . In Na ₄ Cl ₅ and Na ₄ Br ₅ , we found unusually short, likely pressure-stabilized, contacts between sodium cations. Ab initio calculations support the analysis of structures, bonding, and properties of the studied halogenides.
Competing Interests: The authors declare no competing financial interest.
(© 2023 The Authors. Published by American Chemical Society.)