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A series of isostructural Ln3O2(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high‐pressure (25–54 GPa) high‐temperature (2000–3000 K) conditions in laser‐heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single‐crystal X‐ray diffraction (SCXRD) as well as corroborated by X‐ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln3O2(CN3) solids are composed of the hitherto unknown CN35− guanidinate anion—deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln3O2(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln3O2(CN3) compounds are recoverable to ambient conditions. The stabilization of the CN35− guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry. [ABSTRACT FROM AUTHOR]

Inorganic ternary metal-C-N compounds with covalently bonded C-N anions encompass important classes of solids such as cyanides and carbodiimides, well known at ambient conditions and composed of [CN] - and [CN 2 ] 2- anions, as well as the high-pressure formed guanidinates featuring [CN 3 ] 5- anion. At still higher pressures, carbon is expected to be 4-fold coordinated by nitrogen atoms, but hitherto, such CN 4 -built anions are missing. In this study, four polycarbonitride compounds (LaCN 3 , TbCN 3 , CeCN 5 , and TbCN 5 ) are synthesized in laser-heated diamond anvil cells at pressures between 90 and 111 GPa. Synchrotron single-crystal X-ray diffraction (SCXRD) reveals that their crystal structures are built of a previously unobserved anionic single-bonded carbon-nitrogen three-dimensional (3D) framework consisting of CN 4 tetrahedra connected via di- or oligo-nitrogen linkers. A crystal-chemical analysis demonstrates that these polycarbonitride compounds have similarities to lanthanide silicon phosphides. Decompression experiments reveal the existence of LaCN 3 and CeCN 5 compounds over a very large pressure range. Density functional theory (DFT) supports these discoveries and provides further insight into the stability and physical properties of the synthesized compounds.

A series of isostructural Ln 3 O 2 (CN 3 ) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high-pressure (25-54 GPa) high-temperature (2000-3000 K) conditions in laser-heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single-crystal X-ray diffraction (SCXRD) as well as corroborated by X-ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln 3 O 2 (CN 3 ) solids are composed of the hitherto unknown CN 3 5- guanidinate anion-deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln 3 O 2 (CN 3 ) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln 3 O 2 (CN 3 ) compounds are recoverable to ambient conditions. The stabilization of the CN 3 5- guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

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.)