Dynamical scattering and electron crystallography - ab initio structure analysis of copper perbromophthalocyanine

Electron diffraction intensity data were collected at 1200 kV from thin epitaxically oriented crystals of copper perbromophthalocyanine (C₃₂Br₁₆CuN₈) in a projection down molecular columns. Measured cell constants for the projection with cmm symmetry are d₁₀₀ = 17.88 (9), b = 26.46 (15) Å. The structure was determined by Fourier refinement after three heavy-atom positions were identified in an initial potential map. In addition to the copper and halogens, all light-atom positions were found. Although the final R value for all data is 0.41, n-beam dynamical calculations for crystal thicknesses corresponding to the estimated sample dimension account for the observed amplitudes that deviate most from their kinematical values.