Crystal supramolecularity: hexagonal arrays of sextuple phenyl embraces amongst chemically diverse compounds

Abstract

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 symmetry, and therefore can be aligned with the principal axis of trigonal crystal lattices. Using the Cambridge Structural Database we report that this does occur in the crystals of a chemically diverse set of compounds, ranging from P(C₆H₄Me-4)₃ and Ph₃CCO₂H, through salts such as [Ph₃PH⁺]₂[Ga₂Cl₆]^2– and [Ph₃PMe⁺]₂[Cu₄I₆]^2–, small molecules such as Ph₃PAlMe₃ and Ph₃POs(CO)₃PPh₃, to larger molecules such as Ph₃SiOTiN(CH₂CH₂O)₃ and Ph₃PCu(µ-SPh)₃U(µ-SPh)₃CuPPh₃(thf)₆ (thf = tetrahydrofuran). The XR₃ moieties and the SPEs occur in hexagonal nets, and this generic crystal structure type (in space groups R, P, Rc, Pc1) is named the hexagonal array of sextuple phenyl embraces, HASPE. The hexagonal nets can be planar, or puckered by expansion or compression along the trigonal axis. The linkages around these 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 considerable flexibility in order to accommodate diverse components, but the integrity of the SPEs is maintained, attesting to their strong contribution to the lattice energy. Lower symmetry portions of molecular structure, and lower symmetry supramolecular motifs such as the CO₂H· · ·HO₂C dimer, are forced to disorder by the dominant hexagonal array of SPEs. Quasi HASPE lattices with lower crystal symmetry have been recognised.