Supramolecular motifs: Concerted multiple phenyl embraces between Ph(4)P(+) cations are attractive and ubiquitous

Examination of the Cambridge Structural Database reveals that Ph(4)P(+) cations in crystals associate through phenyl-phenyl nonbonded interactions which are attractive, concerted, and widespread. Intermolecular phenyl-phenpl conformations, which are offset-face-to-face (off), edge-to-face (ef) or vertex-to-face (vf), combine in five classes of supramolecular motifs for {Ph(4)P(+)}(2) pairs, namely the sextuple phenyl embrace (SPE) with (ef)(6) and offset sextuple phenyl embrace (OSPE) containing (off)(1)(ef)(2)(ef/vf)(2), the translational quadruple phenyl embrace (TQPE) with (ef)(4), the parallel quadruple phenyl embrace (POPE) with (off)(1)(vf)(2), and the double phenyl embrace (DPE) with (off)(1). Typical intermolecular attractive energies (kJ per mol of {Ph(4)P(+)}(2)) for these motifs are SPE 85, OSPE 57, TQPE 70, PQPE 41, DPE 34. There is strong interpenetration of the cations in these motifs: 489/770 structures in the CSD have P ... P less than or equal to 7 Angstrom (spherical Ph(4)P(+) has a van der Waals diameter of 13.6 Angstrom). Of the 812 instances of P ... P less than or equal to 7 Angstrom, 86% are SPE, 10% are OSPE, 2% are TQPE, and only 2% are unclassified. Average P ... P separations in the PQPE and DPE are 8.3 Angstrom. Centrosymmetry is prevalent in all except the TQPE, which has implications for the engineering of noncentric crystals.