The elusive cyclotriphosphazene molecule and its Dewar benzene-type valence isomer (P₃N₃)

Although the chemistry of phosphorus and nitrogen has fascinated chemists for more than 350 years, the Hückel aromatic cyclotriphosphazene (P₃N₃, 2) molecule-a key molecular building block in phosphorus chemistry-has remained elusive. Here, we report a facile, versatile pathway producing cyclotriphosphazene and its Dewar benzene-type isomer (P₃N₃, 5) in ammonia-phosphine ices at 5 K exposed to ionizing radiation. Both isomers were detected in the gas phase upon sublimation via photoionization reflectron time-of-flight mass spectrometry and discriminated via isomer-selective photochemistry. Our findings provide a fundamental framework to explore the preparation of inorganic, isovalent species of benzene (C₆H₆) by formally replacing the C─H moieties alternatingly through phosphorus and nitrogen atoms, thus advancing our perception of the chemical bonding of phosphorus systems.