The cation in 3 belongs to the well-known family of bis(phosphino)iminium cations (PPN + cations), but is the first all P/N example featuring a +4 molecular charge. Despite this high charge, 3 exhibits no sensitivity towards ambient atmosphere in the solid or solution phases, and, interestingly, also features a LUMO comprised of P-N σ* antibonding orbitals localized primarily inside the cage (Figure , SI).