Formation of the elusive tetrahedral P 3 N molecule.

The tetrahedral 1,2,3-triphospha-4-azatricyclo [1.1.0.0 2,4 ] butane (P 3 N) molecule-an isovalent species of phosphorus (P 4 )-was prepared in low-temperature (5 K) phosphine-nitrogen ices and was identified in the gas phase through isomer-selective, tunable, soft photoionization reflectron time-of-flight mass spectrometry. Theoretical calculations reveal that the substitution of a single phosphorus atom by nitrogen in the P 4 molecule results in enhanced spherical aromaticity while simultaneously increasing the strain energy from 74 to 195 kJ mol -1 . In P 3 N, the P─P bond is shortened compared to those in P 4 by 3.6 pm, while the P─N─P bond angle of 73.0° is larger by 13.0° compared to the P─P─P bond angle of 60.0° in P 4 . The identification of tetrahedral P 3 N enhances our fundamental understanding of the chemical bonding, electronic structure, and stability of binary, interpnictide tetrahedral molecules and reveals a universal route to prepare ring strained cage molecules in extreme environments.