Why do crystal structures waste molecular inversion symmetry?

Abstract

Image reproduced with permission from Abbie TrewinOther articles published in this issue include:Dipyrrin based homo-and hetero-metallic infinite architectures Stéphane A. Baudron, CrystEngComm, 2010, Single-component molecular crystal structures containing centrosymmetric molecules with noncentrosymmetric crystallographic site symmetry are retrieved from the Cambridge Structural Database. The distribution amongst space group types is comparable to that for molecular crystals in general, except that there is a significant decrease in the proportion of triclinic structures. The structures are analysed in terms of the symmetrical relationships between them and some specific chemical circumstances that lead to wasted molecular inversion symmetry are identified: (1) planar centrosymmetric molecules form locally centrosymmetric pairs through face-to-face (p-p) interactions and these pairs pack through edge-to-face interactions; (2) molecules form layers that are locally centrosymmetric but the symmetry within the layers is not compatible with the symmetry of the interlayer interactions. Although the non-centrosymmetric environments of isolated centrosymmetric molecules seem to be unusual, the symmetries of the identified structural fragments and the interactions between them are quite normal. ; Fax: +45 6615 8780; Tel: +45 6550 2545 † Electronic supplementary information (ESI) available: A list of refcodes for the structures retrieved from the CSD, together with their structural classes. See

Four Polymorphs of Methyl Paraben: Structural Relationships and Relative Energy Differences

“…We have previously reported a few similar examples 36−38 and assume that many Z ′ > 1 structures can be interpreted in a similar fashion. The formation of crystal structures with “wasted molecular inversion symmetry” recently discussed by Bond 62 is an analogous phenomenon. The analysis of 1-I was based on a geometry comparison of its distinct molecular environments with the XPac method, which has the advantage that individual data points and molecule/molecule arrangements are intrinsically linked together.…”

Which conformations make stable crystal structures? Mapping crystalline molecular geometries to the conformational energy landscape

“…Molecular symmetry may be benecial for close packing and it has been shown that molecules that adopt a centrosymmetric geometry in their crystal structure almost exclusively crystallise with molecules on crystallographic special positions. 38,39 However, it is not clear what role symmetry plays in determining the conformer that a molecule adopts. Here, we observe that, of the six molecules with potential centrosymmetry (FAHNOR, ODNPDS, FIBKUW, GALCAX, CELHIL SIKRIN), ve adopt centrosymmetric or nearly centrosymmetric conformations in their crystal structures.…”

Solid-state transformations in the β-form of chlorpropamide on cooling to 100 K

“…because of unrecognized crystal twinning (Herbstein, 1964). Structures with Z 0 > 1 can indicate that the crystal is actually a domain intergrowth of two or more different polymorphs (Bernstein et al, 2008;Bishop & Scudder, 2009;Bond, 2009;Bond et al, 2007;Zorky & Nesterova, 1986, 1993. Structures with high Z 0 values are often characterized by pseudosymmetry or modulation (Kuleshova et al, 2003;Schö nleber et al, 2003) and can be modified, distorted or modulated versions of the lower Z 0 structures (Bernstein et al, 2008).…”

“…The phenomenon of the conformational polymorphism or contact conformery (the occurrence of different conformers of the same molecule in different crystal forms) has been attracting attention for a long time (see e.g. Anderson et al, 2008;Bernal, 2007;Bernstein, 1987Bernstein, , 2002Bishop & Scudder, 2009;Bond, 2010;Brock & Minton, 1989;Gavezzotti, 2008;Hao et al, 2005;Lavut et al, 1981;Leonidov et al, 1993;Nangia, 2008;Nichol & Clegg, 2007;Pidcock, 2006;Vande Velde et al, 2010;Zorky & Razumaeva, 1979). X-ray crystal structures of conformational polymorphs help to understand the interplay of intramolecular (conformer) and intermolecular (lattice) energy in the crystallization and stability of polymorphs.…”