Stabilization Of The CN₃⁵⁻ Anion In Recoverable High‐pressure Ln₃O₂(CN₃) (Ln=La, Eu, Gd, Tb, Ho, Yb) Oxoguanidinates

Abstract

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.

Synthesis of LaCN3, TbCN3, CeCN5, and TbCN5 Polycarbonitrides at Megabar Pressures

“…The refinement against SCXRD data (Figures S1−S4) yields very good agreement factors (see Tables S2−S5 and CIFs for the full crystallographic data). The carbon atoms in the discovered polycarbonitrides originate from the diamond anvils, well known to be able to act as a carbon source and participate in chemical reactions. ,,,− The description of other reaction products, e.g. binary polynitrides, will be discussed elsewhere.…”

“…Ternary metal–C–N compounds with covalently bonded C–N anions at ambient conditions encompass important classes of solids such as cyanides (with CN – anions) , and carbodiimides (with NCN 2– anions). − Recently, this family of species was extended with the discovery of the CN 3 5– anion, synthesized at mild pressures (25–54 GPa) and recoverable to ambient conditions. , Knowing that C–N compounds built of CN 4 tetrahedra were obtained at pressures above 70 GPa, as well as the fact that mild pressures (up to 54 GPa) are insufficient for the formation of C–N anions with a tetra-coordinated carbon, the stabilization of CN 4 8– units, or/and the formation of polycarbonitrides built of corner/edge-sharing CN 4 tetrahedra in ternary metal–C–N systems are expected at pressures above 70 GPa. The discovery of such compounds might be interesting not only for chemical and materials sciences but also for planetary sciences since these solids can potentially be formed at the boundaries between the rock core and the methane-ammonia-rich mantle of ice-giant planets.…”

High-Pressure oC16-YBr3 Polymorph Recoverable to Ambient Conditions: From 3D Framework to Layered Material

“…High-pressure synthesis in the 10–100 GPa pressure range has led to the discovery of many exotic compounds with outstanding physical properties. − Pressure can be considered an effective tool for band gap tuning, with its application adding an opportunity to affect the optical properties of synthetic materials. According to theoretical predictions, high-pressure yttrium halides have a good perspective of applications: YCl and Y 2 Cl 3 have been identified as promising quasi-2D and quasi-1D electride materials, respectively, whereas YBr 3 or YI 3 as materials for vdW heterostructure electronic devices. ,− However, experimental data for yttrium halides at high pressures are still limited.…”