DIFFRACTION STUDIES ON METAL-FREE PHTHALOCYANINES (BETA-H2PC AND X-H2PC)

The crystal structure of the beta-polymorph of metal free phthalocyani ne (beta-H2Pc) was redetermined from single crystals to obtain precise placements of the hydrogen atoms and a precise model for the X-polymo rph (X-H2Pc) for which only limited data from different diffraction te chniques are available. Partial occupancy for the hydrogens fixed to t he nitrogens in the inner ring was found leading to a highly symmetric phthalocyanine molecule. Careful evaluation of X-ray, electron and ne utron diffraction data for X-H(2)Pe results in an orthorhombic unit ce ll with a = 2.10 nm, b = 0.491 nm, c = 2.31 nm, space group Pna2(1) co ntaining four molecules in contrast to a recent determination of Oka a nd Okada who proposed a monoclinic unit cell with two molecules. As ex pected the phthalocyanine molecules pack in stacks. The overlap of mol ecules within one stack matches the current ideas for photosensitive p hthalocyanine pigments.