Dibenzo[<i>def</i>,<i>pqr</i>]tetraphenylene (bi-4,5-phenanthrylene)

C28H16 , M r = 352.44, monoclinic, Cc, a = 30.492(4), b = 7.405(4), c = 16.362 (4)A, fl = 105.30 (1) °, U = 3563.5 A 3, Z = 8, D x = 1.314 Mg m -3, ~(Mo K~t) = 0.069 mm -1. The structure was solved by incorporating trio relations into the starting set for multisolution direct methods, and refined to R = 0.048 for 3947 unique observed reflexions. The molecule shows a distorted tub conformation. The phenanthrene moieties are twisted considerably. The racemate consists of helical PP and MM enantiomers. Introduction. Cyclooctatetraene and its derivatives show non-planar tub conformations (Fray & Saxton, 1978). Tetraphenylene, a tetrabenzocyclooctatetraene, has the same geometry (Irngartinger & Reibel, 1981). Some bridged tetraphenylene derivatives have been synthesized and non-planar conformations postulated from spectroscopic data (Hellwinkel & Haas, 1979; Hellwinkel, Reiff & Nykodym, 1977). We determined the structure of dibenzo(def, pqrltetraphenylene (I), a bi-4,5-phenanthrylene (Thulin & Wennerstr6m, 1977), to establish the molecular conformation.