2,2 '',3,3 '',4,4 '',5,5 ''-Octaphenyl-1,1 ':4 ',1 ''-terphenyl and 2 ',3 ',5 ',6 '-tetrafluoro-2,2 '',3,3 '',4,4 '',5,5 ''-octaphenyl-1,1 ':4 ',1 ''-terphenyl

The title compounds, C66H46, (I), and C66H42F4, (II), are polyphenylated arylenes synthesized by one-step Diels-Alder cycloaddition reactions. In both structures, all molecules lie on crystallographic inversion centers. In the case of (I), there are two half-molecules present in the asymmetric unit, (IA) and (IB); the geometry of each half-molecule differs principally in the magnitudes of the dihedral angles between mean planes fitted through the central aryl ring and the pendant phenyl rings. The crystal used was a non-merohedral twin, with a refined twin scale factor of 0.460 (8). The dihedral angle between the plane of the central tetrafluorinated ring and the adjacent tetraphenylated ring in (II) is 83.87 (4)degrees, significantly greater than the dihedral angles of 49.89 (12) and 54.38 (10)degrees found in the two half-molecules in (IA) and (IB), respectively, and attributed to intermolecular C-H center dot center dot center dot F hydrogen bonding in (II). Intermolecular C-H center dot center dot center dot pi bonding is found in (I). Two interactions have the C-H bond oriented towards the centroid (Cg) of a butadiene fragment of a phenyl ring; both H center dot center dot center dot Cg distances are approximately 2.68 angstrom and the interactions connect adjacent molecules into stacks in the c-axis direction. The composition of the stacks alternates, i. e. (IA)-(IB)-(IA)-(IB) etc. A third, weaker, C-H center dot center dot center dot pi interaction and a phenyl-phenyl close contact connect each end of the long molecular axes of (IB) with an adjacent molecule of (IA) into chains which run perpendicular to the (140) and ((1) over bar 40) planes. C-H center dot center dot center dot F interactions in (II) have the most profound influence on the molecular and crystal structure, the main effect of which is the above-mentioned increase in the dihedral angle between the plane of the central tetrafluorinated ring and the adjacent tetraphenylated ring. C-H center dot center dot center dot F interactions have refined H center dot center dot center dot F distances of 2.572 (15) and 2.642 (16) angstrom, with approximate C-H center dot center dot center dot F angles of 123 and 157 degrees, respectively. These form a hydrogen-bonded ribbon structure which propagates in the b-axis direction.