Analysis of the diffuse X-ray scattering from substitutionally disordered molecular crystals: monoclinic 9-bromo-10-methylanthracene

Model calculations of random and correlation distributions of diffuse X-ray scattering are used to determine the correlations between molecular sites of a substitutionally disordered molecular crystal. The correlation coefficients are varied until qualitative agreement is obtained between the calculated diffuse scattering and that measured using Weissenberg film techniques. This procedure was used to determine the correlation coefficients of the monoclinic form of 9-bromo-10-methylanthracene, C₁₅H₁₁Br. The four nearest-neighbour correlations were found to be a = 0.4 (0.1), b = 0.20 (0.05), c = 0.0 (0.05) and d = 0.05 (0.03), respectively. These values imply that the probability of bromine-methyl contacts between neighbouring molecules is greater than that for a random distribution of molecules and that the probabilities of bromine-bromine and methyl-methyl contacts are smaller than for the random distribution.