Abstract
BackgroundStructural systematics is the comparison of sets of chemically related crystal structures with the aim to establish and describe relevant similarities and relationships. An important topic in this context is the comparison of hydrogen-bonded structures (HBSs) and their representation by suitable descriptors.ResultsThree different description methods for HBSs are proposed, a graphical representation, a symbolic representation and connectivity tables. The most comprehensive description is provided by a modified graph of the underlying net topology of an HBS which contains information on the multiplicity of links, the directionality and chemical connectivity of hydrogen bonds and on symmetry relations. By contrast, the alternative symbolic representation is restricted to essential properties of an HBS, i.e. its dimensionality, topology type and selected connectivity characteristics of nodes. A comparison of their connectivity tables readily identifies differences and similarities between crystal structures with respect to the intermolecular interaction modes adopted by their functional groups. The application of these methods to the known polymorphs of sulfathiazole and sulfapyridine is demonstrated and it is shown that they enable the rationalisation of previously reported and intricate relationships.ConclusionsThe proposed methods facilitate the comprehensive description of the most important relevant aspects of an HBS, including its chemical connectivity, net topology and symmetry characteristics, and they represent a new way to recognise similarities and relationships in organic crystal structures.Graphical Graphical Representation of mixing of structures StzIV and StzV to give structure StzIII.Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-014-0076-x) contains supplementary material, which is available to authorized users.
Highlights
Structural systematics is the comparison of sets of chemically related crystal structures with the aim to establish and describe relevant similarities and relationships
The type of the net is denoted by the three-letter RCSR (Reticular Chemistry Structure Resource) symbol [33] or in case of a novel topology its point symbol [34] can be used instead
The topological net of an hydrogen-bonded structures (HBSs) exhibits the following additional and important characteristics: 3. individual H-bonds are indicated by arrows (H → A) placed next to a link; 4. the underlying H/A combination(s) and a symbol for the associated symmetry element are given for each link in the legend of the diagram
Summary
Structural systematics is the comparison of sets of chemically related crystal structures with the aim to establish and describe relevant similarities and relationships. The structural systematics approach is used to increase our knowledge and understanding of the assembly of organic molecules into crystal structures [1,2,3,4,5,6,7,8,9,10]. Such investigations are carried out on polymorphs, solvates, salts and molecular complexes, in which a particular molecule can occur in different crystal structure environments, and with families of compounds, whose molecular structures are very closely related, through small but systematic modifications to a parent molecule. Even though geometrically similar structure patterns associated with hydrogen bonding are regularly identified as an integral part of an XPac study, the most fundamental property of a hydrogen-bonded
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