Single crystals of 3 suitable for single crystal X-ray diffraction were grown in the glovebox by slow evaporation of n-hexane at -35 °C (Figure ). This pyramidal structure at phosphorus is reflected in the single crystal structure for 3, in which the sum of the angles around P1 is 313.0°, with N1-N2 and N1-P1 bond lengths of 1.258(3) and 1.7494(18) Å, respectively. By contrast, the sum of the angles around the analogous nitrogen centre in related triazenes has been reported to be very close to 360°, with N=N bond lengths of 1.270(1) Å, 1.281(7) Å, and 1.288( ), highlighting the increased planarisation in these species.