PREDICTION OF POSSIBLE CRYSTAL-STRUCTURES FOR C-CONTAINING, H-CONTAINING, N-CONTAINING, O-CONTAINING AND F-CONTAINING ORGANIC-COMPOUNDS

A procedure is reported for the prediction of dense crystal structures of C-, H-, N-, O-, and F-containing organic compounds in the primitive triclinic, monoclinic, and orthorhombic space groups with Z less-than-or-equal-to 4. The crystal environments of molecules in 242 crystal structures have been analyzed to determine the common coordination sphere patterns. This led to the development of the MOLPAK (MOLecular PAcKing) program, which uses a rigid-body molecular structure probe to build packing arrangements (possible crystal structures) in the various space groups. A MOLPAK search, which involves the investigation of all unique orientations of a central molecule and the construction of the appropriate coordination patterns about the central molecule, provides a 3-D map of minimum unit cell volume as a function of the orientation of the central molecule. MOLPAK uses a repulsion-only potential and a preset threshold to place molecules in contact with each other. The 5-10 smallest volume packing arrangements from a search are subjected to a lattice energy minimization refinement with the WMIN program to yield possible crystal structures. The results are described from the analyses of several known compounds starting with the crystal molecular structures as the MOLPAK search probes in the P1BAR, P2(1), P2(1)/c, and P2(1)2(1)2(1) space groups. In addition, several examples are given in which the search probes were created by AM1 geometry optimization of preliminary molecular models. More extensive data are given in supplementary tables.