9,10,12,13,14,15-Hexahydro-11H-9,10[1′,3′]cyclopentanthracene in two modifications

The title compound was prepared by catalytic hydrogenation of the 4πs + 4πs photochemical cycloadduct between anthracene and cyclopentadiene to confirm the structure of the cycloadduct. Two different crystal morphologies were obtained. Bond distances and angles for the P21/c modification, which contains one molecule in the asymmetric unit, agree with ab initio calculations. Relative to typical C-C single bonds, the interannular bonds between the bridgehead carbons of the anthracene- and cyclopentane-derived fragments are elongated (observed to average 1.581 Å and calculated to be 1.585 Å and 1.583 Å by RHF and MP2 theories, respectively), but other bond parameters are unexceptional. The C2/c structure contains one-half of a molecule disordered about an axis of pseudosymmetry. Bonding parameters in this structure are distorted due to the disorder which is only partially resolved. The origin of the disorder is considered in light of the crystallographic packing interactions.