Insertion of the intermediately formed carbene-analogous PX24 ion (X = Br, I) into one of the P-P bonds of the P4 tetrahedron led to the P5X2+ ion - the 1st example of the previously unknown class of phosphorus-rich binary P-X cations. The crystal structure of [P5Br2]+[Al{OC(CF3)3}]- was detd. and mol. structure calcns. were performed on both the bromide and iodide analogs. [on SciFinder (R)]