Crystal packing of hydrocarbons. Effects of molecular size, shape and stoichiometry

Abstract

275practically completely explained in terms of modulations of the average structure which are of the £2 symmetry, even though the average crystal structure corresponds to a frozen-in £, modulation.We argue that the short-range order, which tends locally to preserve the c-glide plane, is due to dipoledipole interactions between molecules. On the other hand, the stability of the lattice over a long range (corresponding to wavevectors close to q = 0) is governed by the short-range repulsive interactions and the ability of the molecules to form a closely packed structure in three different crystallographic planes. In agreement with the general conclusions of Kitaigorodsky (1973) the BEMB2 molecules are more easily able to do this in the space group P21 than in Pc. The 'hole' represents a range of wavevectors for which the strain from the packing forces, as a result of the local breaking of the P21 symmetry, outweighs the energy gained from the short-range ordering of the molecular dipoles. sities, a partitioning of the calculated PE over contact types, the average PE per atom in the molecule, and the number of contacts per atom within a 7/k sphere. The molecular coordination number in hydrocarbon crystals is studied by partitioning the PE in successive shells of four to twelve neighbour molecules; the first (four-molecule) shell contributes 33 to 77% of PE, depending on various factors; the contribution of the twelve-molecule shell is invariably close to 100%.

A Practical Guide to the Design of Molecular Crystals

“…Kitaigorodskii’s analysis of known molecular crystal structures revealed that most aromatic molecules exhibit a packing coefficient between 0.6 and 0.8, a range that was later corroborated using database analyses and statistical methods . Orelkin ( c .…”

“…Kitaigorodskii's analysis of known molecular crystal structures revealed that most aromatic molecules exhibit a packing coefficient between 0.6 and 0.8, a range that was later corroborated using database analyses and statistical methods. 59 Orelkin (c. 1930) proposed that densely packed molecular crystals are obtained when the "bumps" of one molecule are inserted in the "hollows" of the neighboring molecule, 50 whereby intermolecular contacts are maximized and void spaces are minimized. The importance of complementary molecular surfaces was also emphasized in 1940 by Pauling and Delbruck.…”

Crystal Engineering: Strategies and Architectures

“…An in-depth overview of computational chemistry in the context of crystal engineering is beyond the scope of this article. Several authors have outlined many of the possibilities and challenges of theoretical supramolecular chemistry (Gavezzotti, 1990;Gavezzotti & Filippini, 1995, 1996Holden, Du & Ammon, 1993;. Gavezzotti (1994) asked the crucial question in a recent review, 'Are crystal structures predictable', and the current answer would have to be 'Sometimes'.…”

Tris(pyrazol-1-yl)-s-triazine (TPT): X-ray crystallographic, computational, and gas-phase electron diffraction studies

“…Qufmica desire to use "engineered" ligands for specific applications in coordination chemistry, the second one is related to the importance of separating the intrinsic properties of molecules, including their geometries, from the consequences of intermolecular interactions in the solid state. Only this approach will allow the determination of crystal packing effects [8,9].…”