REDETERMINATION OF THE STRUCTURE OF BI(9,10-DIHYDRO-9,10-ANTHRACENEDIYL) AT 198-K

C28H20, M(r) = 356.4, orthorhombic, Pbca, a = 8.101 (1), b = 12.034 (2), c = 18.753 (6) angstrom, V = 1828.1 (7) angstrom 3, Z = 4 (the asymmetric unit is half a molecule), D(x) = 1.295 g cm-3, Mo K-alpha (lambda = 0.71073 angstrom), mu = 0.68 cm-1, F(000) = 752, T = 198 K, R = 0.0416 and wR = 0.0442 for 1162 reflections (F0 greater-than-or-equal-to 6-sigma\F0\). The molecule consists of two anthracene units linked together through two bonds. The bond angles at C9 and C10 appear to be normal. The two symmetrically equivalent bonds, C9-C10' and C10-C9', are unusually long, 1.618 (3) angstrom, compared to a C(sp3)-C(sp3) distance of 1.54 angstrom. The elongation may be attributed to repulsion between the aromatic rings at the two bridging atoms. The agreement with the room-temperature structure (see Related literature) is excellent; bond distances and angles are within 3-sigma or less. The closest non-bonding intramolecular distances, C(4a)-C(8a') and C(9a)-C(10a') are 2.742 (3) and 2.721 (3) angstrom, respectively, vs 2.746 (3) and 2.732 (3) angstrom at room temperature (these distances were incorrectly reported as 2.827 and 2.832 angstrom). The dihedral angles are also in agreement, 135.2 (3) vs 135.4 (3)-degrees (incorrectly stated as 131.2-degrees). The rigid-body motion was almost isotropic; librational corrections to all C-C bonds = 0.001 angstrom (sigma-bond = 0.003 angstrom). A possible cause of the apparent anisotropy of the libration in the room-temperature model could be an inadequate isotropic decay correction of the intensity data, which could be compensated by the refinement of the anisotropic thermal parameters.