Two novel yttrium nitrides, YN₆ and Y₂N₁₁, were synthesized by direct reaction between yttrium and nitrogen at 100 GPa and 3000 K in a laser‐heated diamond anvil cell. High‐pressure synchrotron single‐crystal X‐ray diffraction revealed that the crystal structures of YN₆ and Y₂N₁₁ feature a unique organization of nitrogen atoms—a previously unknown anionic N₁₈ macrocycle and a polynitrogen double helix, respectively. Density functional theory calculations, confirming the dynamical stability of the YN₆ and Y₂N₁₁ compounds, show an anion‐driven metallicity, explaining the unusual bond orders in the polynitrogen units. As the charge state of the polynitrogen double helix in Y₂N₁₁ is different from that previously found in Hf₂N₁₁ and because N₁₈ macrocycles have never been predicted or observed, their discovery significantly extends the chemistry of polynitrides.

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.

We report the high-pressure synthesis and the equation of state (EOS) of a novel nickel carbide (Ni₃C). It was synthesized in a diamond anvil cell at 184(5) GPa through a direct reaction of a nickel powder with carbon from the diamond anvils upon heating at 3500 (200) K. Ni₃C has the cementite-type structure (Pnma space group, a = 4.519(2) Å, b = 5.801(2) Å, c = 4.009(3) Å), which was solved and refined based on in-situ synchrotron single-crystal X-ray diffraction. The pressure-volume data of Ni₃C was obtained on decompression at room temperature and fitted to the 3rd order Burch-Murnaghan equation of state with the following parameters: V₀ = 147.7(8) ų, K₀ = 157(10) GPa, and K₀′ = 7.8(6). Our results contribute to the understanding of the phase composition and properties of Earth’s outer core.

A gasket is an important constituent of a diamond anvil cell (DAC) assembly, responsible for the sample chamber stability at extreme conditions for X-ray diffraction studies. In this work, we studied the performance of gaskets made of metallic glass Fe_0.79Si_0.07B_0.14in a number of high-pressure X-ray diffraction (XRD) experiments in DACs equipped with conventional and toroidal-shape diamond anvils. The experiments were conducted in either axial or radial geometry with X-ray beams of micrometre to sub-micrometre size. We report that Fe_0.79Si_0.07B_0.14metallic glass gaskets offer a stable sample environment under compression exceeding 1 Mbar in all XRD experiments described here, even in those involving small-molecule gases (e.g.Ne, H₂) used as pressure-transmitting media or in those with laser heating in a DAC. Our results emphasize the material's importance for a great number of delicate experiments conducted under extreme conditions. They indicate that the application of Fe_0.79Si_0.07B_0.14metallic glass gaskets in XRD experiments for both axial and radial geometries substantially improves various aspects of megabar experiments and, in particular, the signal-to-noise ratio in comparison to that with conventional gaskets made of Re, W, steel or other crystalline metals.