Abstract Polyhedral nitrogen containing molecules such as prismatic P 3 N 3 - a hitherto elusive isovalent species of prismane (C 6 H 6 ) - have attracted particular attention from the theoretical, physical, and synthetic chemistry communities. Here we report on the preparation of prismatic P 3 N 3 1,2,3-triaza-4,5,6-triphosphatetracyclo2.2.0.0 2,6 .0 3,5 hexane by exposing phosphine (PH 3 ) and nitrogen (N 2 ) ice mixtures to energetic electrons. Prismatic P 3 N 3 was detected in the gas phase and discriminated from its isomers utilizing isomer selective, tunable soft photoionization reflectron time-of-flight mass spectrometry during sublimation of the ices along with an isomer-selective photochemical processing converting prismatic P 3 N 3 to 1,2,4-triaza-3,5,6-triphosphabicyclo2.2.0hexa-2,5-diene (P 3 N 3 ). In prismatic P 3 N 3 , the P–P, P–N, and N–N bonds are lengthened compared to those in, e.g., diphosphine (P 2 H 4 ), di-anthracene stabilized phosphorus mononitride (PN), and hydrazine (N 2 H 4 ), by typically 0.03–0.10 Å.  These findings advance our fundamental understanding of the chemical bonding of poly-nitrogen and poly-phosphorus systems and reveal a versatile pathway to produce exotic, ring-strained cage molecules.