Anisotropic crystal growth in flat and nonflat systems: The important influence of van der Waals contact molecular stacking on crystal growth and dissolution

The crystal structures and crystal morphology of the mono-semicarbazone of 9,10-phenanthraquinone and nine of its solvates were examined to probe the mechanism of crystal growth of flat molecules. Three of the solvates were isomorphous, did not have stacked structures, and grew as blocks. Six of the solvates had stacked structures and grew as needles. A centroid distance based method for the detection of van der Waals (vdW) contact stacking is described. Nonflat carbamazepine (CBZ) forms I, III, and VI, 4-hydroxy-N-phenylbenzenesulfonamide, and a polymorph of 1,4-diphenyl-2H-cyclopenta[d]pyridazine all exhibited needle growth and have structures which maximize vdW contact stacking in the needle growth direction. The experimentally reported anisotropic dissolution of CBZ form I has been simulated using molecular dynamics. The intermolecular interactions have been analyzed using Gavezzottis PIXEL program. Dispersion force interactions between the molecules are most important within the stacks. A crystal growth mechanism driven by the dispersion force rather than hydrogen bonding is suggested for both flat and nonflat molecules.