The coordination chemistry of Lewis acidic phosphorus centers with a wide variety of donors to form typical Lewis donor-acceptor complexes has become a pivotal and rapidly growing field contributing to the understanding of fundamental phosphorus chemistry. Complexes of the acceptor unit 1 have been reported for the methylenediylphosphenium cation (in [1a]AlCl₄) or phosphadiazonium (e.g in [1b]OTf and [1c]OTf) cations (OTf = trifluoromethanesulfonate), and the phosphenium unit 2 is envisaged as the acceptor in the cations of [2a]Cl (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene), [2b]OTf [DMAP = 4-(dimethylamino)pyridine)] and [2c]OTf.  Although salts of tricoordinate phosphonium 3 cations are well known, the first complexes (3a and 3b) involving the acceptor unit 3 were only recently reported and extended to the ligand stabilized thiophosphonium cation 3c and 3d.  This fundamentally important development of non-metal Lewis acceptor centers in the chemistry of phosphorus has now been diversified with the discovery of complexes involving the dicationic center 4 as observed in the ligand stabilized Me₃P²⁺ cations such as 4a and 4b.