contrast to the triaminomethyl carbenium ion which adopts a planar structure, a diaminophosphanyl substituent attached at the electron-deficient carbenium center introduces anionic character. As a consequence the tris(diaminophosphanyl)carbenium ion possesses an unusual equilibrium structure with three different PC bond lengths. The bonding situation is rationalized in the framework of contributing donor-acceptor structures to the overall bonding. A similar bonding situation is obtained for the phosphanyl substituent attached to an electron-deficient center.