To probe the differences between azophosphine 3 and its N-containing analogue, triazene A (Table ), density functional theory calculations and natural bond orbital (NBO) analyses were carried out (see SI for details). The computed bond metric data shows 3 has a shorter N=N bond (1.239 Å) than A (1.247 Å); this is corroborated by a Wiberg bond index (WBI) of 1.84 for the N=N bond of 3, and 1.67 for A. Both metrics are consistent with reduced donation from the pnictogen lone pair into the N=N π* orbital for 3 compared to A. This was further supported by examination of the donor/acceptor interactions of the pnictogen lone pair into the N=N π* orbital; the value of 4.73 kcal•mol -1 for 3 is significantly smaller than 79.58 kcal•mol -1 for A. Additionally, the sum of the angles around the phosphorus centre in 3 (307.3°) is significantly lower than the angles around the nitrogen centre in A (357.6°), indicative of a pyramidal structure around the phosphorus centre, compared to the highly planarized triazene. This is consistent with the crystal structures discussed above. Given the aforementioned diagonal relationship between phosphorus and carbon, 3 was also compared to carbon analogue B (Table ). The computed N=N bond length (1.232 Å) and WBI (1.86) for B places 3 in between A and B for both. These values are consistent with B possessing significant N=N double bond character and N-C(H) single bond character (computed bond length of 1.465 Å). By contrast, the N=N bonds of 3 and A are both longer than the additive covalent radii for an N=N double bond, and the N-P/N-N bonds shorter, indicative of the increased delocalisation in these structures. These data underlines the structure of 3 exists somewhere between that of triazene A, and the carbon equivalent B.