Diffraction studies on metal free phthalocyanines (β-H2Pc and X-H2Pc)

Abstract

The crystal structure of the β-polymorph of metal free phthalocyanine (β-H2Pc) was redetermined from single crystals to obtain precise placements of the hydrogen atoms and a precise model for the X-polymorph (X-H2Pc) for which only limited data from different diffraction techniques are available. Partial occupancy for the hydrogens fixed to the nitrogens in the inner ring was found leading to a highly symmetric phthalocyanine molecule. Careful evaluation of X-ray, electron and neutron diffraction data for X-H2Pc results in an orthorhombic unit cell with a=2.10 nm, b=0.491 nm, c=2.31 nm, space group Pna21 containing four molecules in contrast to a recent determination of Oka and Okada who proposed a monoclinic unit cell with two molecules. As expected the phthalocyanine molecules pack in stacks. The overlap of molecules within one stack matches the current ideas for photosensitive phthalocyanine pigments.