CRYSTAL SUPRAMOLECULARITY - HEXAGONAL-ARRAYS OF SEXTUPLE PHENYL EMBRACES AMONGST CHEMICALLY DIVERSE COMPOUNDS

The sextuple phenyl embrace (SPE) occurs widely between molecules with XR3 (R = aryl) moieties, and has at least quasi-three-fold symmetry. The SPE can have exact 3 symmetry, and therefore can be aligned with t he principal axis of trigonal crystal lattices. Using the Cambridge St ructural Database we report that this does occur in the crystals of a chemically diverse set of compounds, ranging from P(C6H4Me-4)(3) and P h3CCO2H, through salts such as [Ph3PH+](2)[Ga2Cl6](2-) and [Ph3PMe+](2 )[Cu4I6](2-), small molecules such as Ph3PAlMe3 and Ph3POs(CO)(3)PPh3, to larger molecules such as Ph3SiOTiN(CH2CH2O)(3) and Ph3PCu(mu-SPh)( 3)U(mu-SPh)(3)-CuPPh3(thf)(6) (thf = tetrahydrofuran). The XR3 moietie s and the SPEs occur in hexagonal nets, and this generic crystal struc ture type (in space groups <R(3)over bar>, <P(3)over bar>, R(3) over b arc$, <P(3)over bar cl>) is named the hexagonal array of sextuple phen yl embraces, HASPE. The hexagonal nets can be planar, or puckered by e xpansion or compression along the trigonal axis. The linkages around t hese hexagonal nets can be further multiple phenyl embraces, or may be elongated substantially. The non-embracing sections of the molecules can occupy the centres of the hexagons. The HASPE lattice type shows c onsiderable flexibility in order to accommodate diverse components, bu t the integrity of the SPEs is maintained, attesting to their strong c ontribution to the lattice energy. Lower symmetry portions of molecula r structure, and lower symmetry supramolecular motifs such as the CO2H ... HO2C dimer, are forced to disorder by the dominant hexagonal arra y of SPEs. Quasi HASPE lattices with lower crystal symmetry have been recognised.