Identification of a prismatic PN molecule formed from electron irradiated phosphine-nitrogen ices.

Polyhedral nitrogen containing molecules such as prismatic PN - a hitherto elusive isovalent species of prismane (CH) - have attracted particular attention from the theoretical, physical, and synthetic chemistry communities. Here we report on the preparation of prismatic PN [1,2,3-triaza-4,5,6-triphosphatetracyclo[2.2.0.0.0]hexane] by exposing phosphine (PH) and nitrogen (N) ice mixtures to energetic electrons. Prismatic PN 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 PN to 1,2,4-triaza-3,5,6-triphosphabicyclo[2.2.0]hexa-2,5-diene (PN). In prismatic PN, the P-P, P-N, and N-N bonds are lengthened compared to those in, e.g., diphosphine (PH), di-anthracene stabilized phosphorus mononitride (PN), and hydrazine (NH), 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.