An uncommon nitride featuring phosphorus surrounded by six nitrogen atoms reveals unexpected metallic behavior. Soft X-ray spectroscopy and density functional theory uncover mixed-valence tantalum and complex TaN bonding, unlocking new insights for future electronic and catalytic technologies.

In this study, the electronic structure and bonding characteristics of P1−x$_{1-x}$Ta8+x$_{8+x}$N13$_{13}$ (x = 0.1–0.15), a compound featuring a high coordination of phosphorus with six nitrogen atoms, are explored. Soft X-ray spectroscopy and density functional theory calculations are employed to investigate the material's electronic properties. The analysis reveals that the material exhibits metallic behavior, which can be attributed to the 5d electronic states of tantalum. It is observed that tantalum exists in mixed valence states, forming two distinct types of TaN bonds: one predominantly covalent and the other with a combination of ionic and covalent characteristics. Both bond types contribute to the metallic properties observed. Additionally, it is found that the valence electrons of tantalum are not fully integrated into the TaN bonds, as supported by electron localization function (ELF) calculations, which show electron localization in narrow channels consisting of three Ta atoms. To the best of our knowledge, we have measured the phosphorus L _β3,β4 XES and L₁-edge XAS for the first time. These findings enhance one's understanding of the complex electronic structure of P1−x$_{1-x}$Ta8+x$_{8+x}$N13$_{13}$ and provide insights into the material's potential applications in electronic devices and electrocatalysis.