Crystal engineering of topochemical solid state reactions

Abstract

Solid state reactions offer a unique opportunity for synthesizing complex molecules with amazing regio- and stereo-specificity otherwise difficult to synthesize by conventional organic synthetic methodologies. In particular, the solid state [2 + 2] reaction is a well studied reaction in terms of a crystal engineering perspective. The main challenge in performing solid state reactions is bringing the molecules into reactive orientations such that the reactive groups are within a certain proximal distance. The out surge in organic and inorganic crystal engineering studies offers several strategies for bringing the molecules together in the crystal lattice. These strategies include from weak interactions (halogen bonds, halogen···halogen, π···π, cation···π) to strong hydrogen bonds (O-H···O, N-H···O, O-H···N and N-H···N) to coordination complexes/polymers. To date many studies are available which use such strategies for conducting single, double, triple or multiple [2 + 2] reactions, [4 + 4] reactions, Diels-Alder reactions and polymerization reactions of acetylene molecules. Some of the crystal engineering strategies include the use of external templates which can be removed after the reaction and some of the other strategies deals with the modification of reactant molecules. In this review, the current status of various strategies will be outlined with respect to the nature of the interactions involved.

Competing hydrogen-bond donors: phenols vs. cyanooximes

“…A key requirement for effective supramolecular synthesis and crystal engineering, 14 is a detailed understanding of the structural 35 balance between different synthons, and therefore it is important to establish how potentially competing interactions will manifest themselves in the solid state. It has previously been shown that both cyanooxime moieties 15 and phenolic -OH groups 16 are more effective hydrogen-bond donors than carboxylic acids.…”

Hydrogen Bonding in Supramolecular Crystal Engineering

“…Up to date, this subject has been highly developed. The advances in supramolecular crystal engineering and improvements of our understanding about intermolecular interactions have enabled chemists to construct solids with predetermined physical properties for solid state reactions [93,94]. The solid state reactions have the advantages of solvent-free conditions that related to green chemistry and stereo-specific reactions with high yields.…”

Metal-Organic Frameworks for Photochemical Reactions

“…The classical work of G. Schmidt and coworkers in 1960s paved away the field of solidstate organic photochemistry as well as crystal engineering [12][13][14]. Due to this historical importance, this double bonds containing spacer and terminal ligands have been incorporated into coordination polymers (CPs) and porous CPs (PCPs) which is also popularly called as metal-organic frameworks (MOFs) to design photo-reactive solids [15][16][17]. The metal-coordination bond offers very important role in directing the organic linkers and/or guest molecules to satisfy the geometry criteria required for the photoreactions.…”