P. Zugenmaier et al., DIFFRACTION STUDIES ON METAL-FREE PHTHALOCYANINES (BETA-H2PC AND X-H2PC), Journal of Materials Science, 32(20), 1997, pp. 5561-5568
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.