Crystal supramolecularity. Multiple phenyl embraces by [PPN](+) cations

Analysis of the 752 crystals in the Cambridge Structural Database containin g [Ph3PNPPh3](+) ([PPN](+)) cations has revealed mutually attractive intera ctions between the cations leading to the formation of supramolecular motif s. The cation is flexible due to P-N-P bending: calculation of single point energies for an idealised [H3PNPH3](+) fragment show a flat energy well fo r the cation, with there being less than 1 kcal mol(-1) difference in energ y between P-N-P angles of 130-180 degrees. The most populated conformation is that with a P-N-P angle in the range 140-145 degrees. The types of inter -cation interaction can be classified by a combination of the N-P ... P ang le, the N-P ... P-N torsion angle and the four intermolecular P ... P dista nces between neighbouring cations. Interactions with an N-P ... P angle of greater than 125 degrees indicate a sixfold phenyl embrace (6PE), whilst th ose at more acute angles form expanded phenyl embraces with neighbouring ca tions either parallel (PEPE) or orthogonal (OEPE). The PEPE and OEPE are di fferentiated by torsion angle or intermolecular P ... P separations. Comput ation of the energies of attraction between the cations gives values in the ranges 7.0-10.5, 7.9-11.1 and 8.6-13.0 kcal mol(-1) for the 6PE, OEPE and PEPE respectively. The individual embraces combine to form zigzag chains of cations leading to either columnar or layered structures. The crystal latt ice formed does not depend on anion size or charge.