Salts containing tetraaryldiphosphine radical cation 1(•+) and dication 1(2+) have been isolated and structurally characterized. Radical 1(•+) has a relaxed pyramidal geometry, while dication 1(2+) prefers a planar, olefin-like geometry with a two-electron π 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 1(•+) is mainly localized on phosphorus atoms, which is supported by theoretical calculation.