P3F92–: An All-Pseudo-π* 2π-Aromatic

A qualitative MO analysis suggests (PH3)3(2-) as a candidate for an all-pseudo-π* 2π-aromatic; however computational studies rule out its existence. Fluorine substitution which increases the contribution of p orbitals on P in the pseudo-π* MO makes (PF3)3(2-) a minimum and an aromatic. The 2π aromaticity arising from the bonding combination of the three pseudo-π* fragment MOs is comparable to that in C3O3(2-) and is another example for the analogy between CO and PF3. The dianion (PF3)3(2-) forms the first example of a three-membered ring with all the vertices constituted by pentacoordinate phosphorus. The ability of PF3 to form the all-pseudo-π* 2π-aromatic system is not shared by the heavier analogues, AsF3 and SbF3.