Salts containing tetraaryldiphosphine radical cation 1(circle+) and dication 1(2+) have been isolated and structurally characterized. Radical 1(circle+) has a relaxed pyramidal geometry, while dication 1(2+) prefers a planar, olefin-like geometry with a two-electron pi bond. The alteration of the geometries of the tetraaryldiphosphine upon oxidation is rationalized by the nature of the bonding. The EPR spectrum showed that the spin density of radical l(circle+) is mainly localized on phosphorus atoms, which is supported by theoretical calculation.