The elusive cyclotriphosphazene molecule and its Dewar benzene–type valence isomer (P 3 N 3 )

Cyclotriphosphazene (P 3 N 3 ) and its Dewar benzene–type isomer were identified on the basis of their photochemical properties. Although the chemistry of phosphorus and nitrogen has fascinated chemists for more than 350 years, the Hückel aromatic cyclotriphosphazene (P 3 N 3 , 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 (P 3 N 3 , 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 (C 6 H 6 ) by formally replacing the C─H moieties alternatingly through phosphorus and nitrogen atoms, thus advancing our perception of the chemical bonding of phosphorus systems.