The crystal structure of Hellwinkel's salt [P(2,2'-biphenylyl) 2 ] z [P(2,2'-biphenylyl) 3 ] 2 (1) is reported and the crystal packing analysed. The cation [P(2,2'-biphenylyl) 2 ] z (P z ) is analogous to Ph 4 P z , and the anion [P(2,2'biphenylyl) 3 ] 2 (P 2 ) is analogous to [M(bipy) 3 ] z complexes, both of which form multiple aryl embraces in crystals, but not previously with each other. The chirality of P 2 is potentially valuable for the resolution of chiral cations. The crystal

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... ularity of 1 is comprised of (1) a P 2 ¼ P 2 sixfold aryl embrace with a calculated energy of 8.9 kcal mol 21 attraction, (2) a tight homochiral embrace P z ¼ P 2 embrace using offsetface-to-face interactions between biphenylyl ligands (calculated attraction 21.0 kcal mol 21 ), (3) a parallel fourfold aryl embrace P z ¼ P z (calculated attraction 1.2 kcal mol 21 ), and (4) several non-standard P z ¼ P 2 embraces (calculated attractions 13.9, 18.3 kcal mol 21 ). Comparisons with related crystals are made. The prognosis for application of P 2 to the resolution of phenylated molecules and cationic metal complexes with phenylphosphonium or phenylarsonium ligands is good. Synthesis Compound 1 was prepared and isolated as previously described. 1 Calculation of inter-ion energies Inter-ion energies were calculated using the summed atom± atom method, with van der Waals and electrostatic compo-