3,4:9,10-Perylenetetracarboxylic dianhydride (PTCDA) by electron crystallography

The crystal structures of the α and β modifications of PTCDA were analyzed as projected structures along the a axes by electron crystallography using an imaging plate. The results for the α modification agree well with the sheet-and-stack structure obtained by X-ray diffraction by M. L. Kaplan et al. (private communication, full set of crystal structure data). Projected onto the (102) plane, which is parallel to the molecular sheets, the long molecular axis makes an angle of 42° with the b axis and the hexagonal benzene rings appear slightly elongated, indicating a slight inclination of the molecular plane from the (102) lattice plane. For the β modification, it was concluded that the molecules are aligned in a herringbone packing scheme on the (102) plane similar to that of the α modification, but with a slightly different angle of the long molecular axis with the b axis (38°).