The crystal and molecular structure of an unusual conjugated hydrocarbon : Cycloocta[1,2,3,4-def]benzo[3,4]cyclobuta[6,7]biphenylene

The conjugated hydrocarbon, cyclo1,2,3,4-def]benzo3,4]cyclobuta6,7]biphenylene, crystallizes in the space group P2₁2₁2₁ with a = 15.136(4), b = 16.453(4), c = 5.584(1) Å, Z = 4, ?_cal = 1.32, ?_obs = 1.31 g cm^?3. The structure was solved by application of direct methods after reducing the dominance of hk0 reflections in starting set selection. Full-matrix, least-squares refinement of 1910 independent data collected with MoK_α radiation on a four-circle diffractometer yielded a final conventional R = 0.068. Bond lengths in this unusual conjugated hydrocarbon range from 1.34 to 1.53 Å. Calculated iterated-Hückel bond lengths that include effects of σ strain reasonably correspond to the observed bond distances, with the largest differences (0.03 Å) occurring in the four membered rings. The molecule is essentially planar, but exhibits an overall bowing that is probably due to crystal packing forces.