Homoatomic cations: From [P 5 ] + to [P 9 ] .

Recent synthetic approaches to a series of [P 9 ] X salts ( X = [F{Al(OR F ) 3 } 2 ], [Al(OR F ) 4 ], and (R F = C(CF 3 ) 3 ); Ga 2 Cl 7 ) overcome limitations in classical synthesis methods that proved unsuitable for phosphorus cations. These salts contain the homopolyatomic cation [P 9 ] + via (I) oxidation of P 4 with NO[F{Al(OR F ) 3 } 2 ], (II) the arene-stabilized Co(I) sandwich complex [Co(arene) 2 ][Al(OR F ) 4 ] [arene = ortho -difluorobenzene ( o -DFB) and fluorobenzene (FB)], or (III) the reduction of [P 5 Cl 2 ][Ga 2 Cl 7 ] with Ga[Ga 2 Cl 7 ] as Ga(I) source in the presence of P 4 . Quantum chemical CCSD(T) calculations suggest that [P 9 ] + formation from [Co(arene) 2 ] + occurs via the nido-type cluster [( o -DFB)CoP 4 ] + , which resembles the isoelectronic, elusive [P 5 ] + . Apparently, the nido-cation [P 5 ] + forms intermediately in all reactions, particularly during the Ga(I)-induced reduction of [P 5 Cl 2 ] + and the subsequent pick up of P 4 to yield the final salt [P 9 ][Ga 2 Cl 7 ]. The solid-state structure of [P 9 ][Ga 2 Cl 7 ] reveals the anticipated D 2d -symmetric Zintl-type cage for the [P 9 ] + cation. Our approaches show great potential to bring other [P n ] + cations from the gas to the condensed phase.