Topology of molecular packings in organic crystals

Using the methods of coordination sequences and of molecular Voronoi-Dirichlet polyhedra, the topological properties of molecular packings and molecular coordination numbers (MCNs) were determined in the crystal structures of 33 575 monosystem organic compounds within the first three coordination spheres. Numerous examples of disagreement between the topology of molecular packing and the system of intermolecular contacts in a crystal structure were found. It is concluded that within the first coordination sphere most of the molecules tend to arrange with MCN = 14, obeying the model of the thinnest covering of space, but molecular packings as a whole tend to be constructed according to one of the close packings.