Benz[cd]indol-2(1H)-one at 298 and 100 K.

Weakly diffracting crystals of benz[cd]indol-2(1H)-one (naphtholactam), C(11)H(7)NO, were unsuitable for data collection by early photographic methods. However, a diffractometer data set collected at room temperature in 1989 was solved and refined. The peak scans were broad, and the results indicated disorder or a satellite crystal. Recent data collection (on another crystal from the same sample) with an area detector at 100 K revealed the same disorder, and made it possible to refine two different, more complete, disorder models. Both models assume an occasional 180° rotation of the nearly planar centrosymmetric cis-lactam dimer. The refinements differ, especially in the anisotropic displacement parameters for the -C(=O)-NH- portion of the molecule. Both models at 100 K give a C-N (`amide') bond distance of 1.38 Å, about 0.04 Å longer than the average distance in saturated γ-lactams in the Cambridge Structural Database. Cohesive packing interactions between molecules include opposing-dipole dimers; the packing may explain the 10:1 ratio favoring the major-occupancy molecule.