Crystal structure of a cyclobutane derivative: 4,8-dibromo-3,7-diketo-3, 4,4a,4b,7,8,8a,8b-octahydrodibenzo- [a,g] -biphenylene

The crystal structure of a cyclobutane derivative, 4,8-dibromo-3,7-diketo-3,4,4a,4b,7,8,8a,8b-octahydrodibenzo-a,g]-biphenylene (C₂₀H₁₄O₂Br₂), has been determined from 1614 intensities collected with a four-circle diffractometer and refined by three-dimensional least-squares techniques. The crystals are monoclinic, space groupP2₁/c, with four molecules in a unit cell of dimensionsa = 10·863 ± 0·006,b = 21·060 ± 0·011,c = 7·772 ± 0·005 Å and β = 105·33 ± 0·04 °. The cyclobutane ring was found to have a bent configuration with a dihedral angle of 157 °.