Crystal Growth Mechanism Determined by Crystallographic and Affine Symmetries. Part II

As shown in Part I, in the case of organic substances with two crystallographically independent molecules, crystallographic and affine symmetries determine crystal growth. The Fourier transform method was used to calculate the theoretical growth forms. The morphological lattice necessary for these calculations can be derived from an affine or klassengleiche supergroup of the structural space group. It can be shown that growth is influenced not only by the geometric effectiveness of the symmetry elements but also by physical factors such as differences in conformation and external factors. The theoretical growth forms were also calculated using attachment energies (Hartman method). A better correspondence to the observed crystals is obtained when the affine symmetries are also considered in these calculations. For these investigations, the crystal structures of 2,3-dichloro-1,4-naphthoquinone, amidopyrine (P1 ), glycolic acid, malonamide and cyanoacetamide (P2 1 /c) were used. All of these structures contain two crystallographically independent molecules in the unit cell.