Nitridation of electron-rich transition metals under pressure can form many binary nitrides with diverse compositions and crystal structures, especially for the W-N system with numerous newly discovered phases. However, because of their unique metastability, most reported W-N products involve complex atomic deficiencies, largely exacerbating the difficulties in structural resolution. Of particular interest is hexagonal $hP10\text{−}{\mathrm{W}}_2{\mathrm{N}}_3$, which has been predicted to be a soft van der Waals (vdW) material but experimentally has shown excellent mechanical properties, likely due to structural misassignment. Here we revisit the high-pressure synthesis and perform a comprehensive study to definitively solve the crystal structure and determine the key properties of this material. We find that it adopts $\mathit{hP}12$ symmetry rather than $\mathit{hP}10$, containing unusual W-W-W trimers. Intricate atomic deficiencies are revealed to be crucially important for stabilizing its crystal structure with an actual composition of $hP12\text{−}{\mathrm{W}}_{4.216}{\mathrm{N}}_{5.278}$. This material is intrinsically metallic and mechanically hard and brittle, opposite to that of a vdW material. It also exhibits superior thermal stability, making it highly suitable for many advanced applications.

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• Defects
• Elastic modulus
• Hardness
• High-pressure studies
• Structural properties
• Crystal structures
• Nitrides
• van der Waals systems
• Acoustic techniques
• Density functional calculations