Supramolecular Isomerism

Abstract

Supramolecular isomers comprise network structures that have identical chemical compositions but differ from one another in their structure. In some instances, the term is also used to describe identical frameworks that contain different counterions, solvent, or guest molecules. Supramolecular isomerism can be observed in both molecular and coordination compounds. Like polymorphism, it results when different, but energetically similar, packing interactions can operate during crystallization. Gaining control on crystallization of a particular isomer remains challenging as both thermodynamic and kinetic factors play a role, and as understanding the full energy profile of a self‐assembly process is extremely difficult. Some important variables within the crystallization system have been identified, including chemical and physical factors, which are described in this chapter. Supramolecular isomers may be considered in four categories: structural, conformational, interpenetrated, and chiral networks. Examples of each are provided. A number of topological approaches have been described over the years, which aid in the description of extended structures. Both graph set and network analyses are useful for this purpose. Crystal engineering aims to control structural characteristics of crystalline materials, with the aim of having greater control over their physical properties. Although hydrogen‐bonded supramolecular synthons have been studied in depth for more than a decade and although coordination bonds are stronger and more directional than other supramolecular interactions, structural uncertainty is still a characteristic of self‐assembled systems. Some structure‐property relationships are emerging, including luminescence and porosity.

Selective Synthesis and Thermodynamic Relations of Polymorphic Co(NCS)2‐4‐Dimethylaminopyridine Coordination Compounds

“…Unfortunately, the energy difference between possible polymorphs or isomers is frequently small, which can lead to the formation of different products under kinetic or thermodynamic control . In this context, a large number of polymorphic and isomeric coordination compounds were reported in the last years , . From a viewpoint of material synthesis this might be of disadvantage but there is also some benefit from these phenomena.…”

Polymorphic Behavior of Two Organic Zwitterions: Two Rare Cases of No Observable Conversion between Polymorphs

“…Despite its first recognition in 1822 by Mitscherlich, 1 the first widely accepted definition, given by McCrone, only appeared in 1965. 2 Since then there has been much debate regarding the significance of isomerism, 3,4 tautomerism, 5 and large conformational changes 6 to this definition, and whether allotropism, 7 amorphous materials, 8 and pseudo-polymorphism should be included in the definition of polymorphs. 9 Nevertheless, the most common and innocuous definition remains that polymorphism 10−12 is when a molecule (or a combination of molecules in the case of multicomponent materials 13 ) can arrange in more than one way in the solid state.…”

Solvent‐Ratio Dependency of Polymorphism of Silver(I) Complexes Containing 1,2,3‐Tris(Isoniconitoyloxy)Benzene

“…These facts make them an attractive research field. Since the first research by Mitscherlich in 1822, understanding the different factors that influence the generation of crystal packing structures of the same chemical composition that can crystallize in at least two kinds of arrangements is of primary importance in terms of isomerism, tautomerism, and substantial conformational changes . The entire higher‐dimensional packing structures of the molecules are not easy to predict due to the influence of the external crystallization condition as well as the subtle weak intermolecular interactions beyond the metal–ligand connectivity on the molecular packing .…”