Crystal structure of acenaphthylene, C12H8, at 80 K by neutron diffraction

Abstract

The crystal structure of acenaphthylene at 80 K has been determined using neutron (λ= 1.238 Å) diffraction data. Though well below the known phase transition (at 130 K) the structure was found to be disordered with space group P2₁nm and a= 7.584(6), b= 7.589(7), and c= 27.851(21)Å. Constrained least-squares refinement led to a residual R of 0.069 using 92 variables for 950 reflections having I_o > 3σ(I_o). The structure has three symmetry-unrelated molecular sites A–C. Site B was found to be totally ordered but sites A and C were disordered. Six different molecular orientations, related approximately by rotations in the molecular plane, were located in site A, while for site C two different orientations were found. The major molecular fragment in site A had an occupancy of 0.554(12) and that for site C an occupancy of 0.708(9).