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 [CN₂]^2– anions, as well as the high-pressure formed guanidinates featuring [CN₃]^5– anion. At still higher pressures, carbon is expected to be 4-fold coordinated by nitrogen atoms, but hitherto, such CN₄-built anions are missing. In this study, four polycarbonitride compounds (LaCN₃, TbCN₃, CeCN₅, and TbCN₅) 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 CN₄ 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 LaCN₃ and CeCN₅ 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.

中文翻译：

---

兆巴压力下合成 LaCN3、TbCN3、CeCN5 和 TbCN5 聚碳氮化物


具有共价键 C-N 阴离子的无机三元金属-C-N 化合物包括重要的固体类别，例如氰化物和碳二亚胺，它们在环境条件下众所周知，由 [CN] ^-和 [CN ₂ ] ^2-阴离子以及高压形成的具有[CN ₃ ] ^5–阴离子的胍盐。在更高的压力下，预计碳将与氮原子配位 4 倍，但迄今为止，这种 CN ₄构建的阴离子仍然缺失。在这项研究中，四种聚碳氮化物化合物（LaCN ₃ 、TbCN ₃ 、CeCN ₅和TbCN ₅ ）在激光加热金刚石砧池中在90至111 GPa的压力下合成。同步加速器单晶 X 射线衍射 (SCXRD) 表明，它们的晶体结构是由以前未观察到的阴离子单键碳氮三维 (3D) 框架构成，该框架由通过二氮或寡氮连接体连接的 CN ₄四面体组成。晶体化学分析表明这些聚碳氮化物化合物与镧系硅磷化物具有相似之处。减压实验揭示了在非常大的压力范围内LaCN ₃和CeCN ₅化合物的存在。密度泛函理论（DFT）支持了这些发现，并为合成化合物的稳定性和物理性质提供了进一步的见解。