Synthetic Clathrate Systems

Abstract

Clathrate compounds traditionally were discovered by happy accident because of the considerable difficulty in predicting and controlling weak intermolecular forces in crystal engineering. This chapter surveys and analyzes the various approaches taken to obtain synthetic organic clathrates, ranging from modification of a known lead compound to the design of an entirely new host from first principles. The clathrate literature has been categorized into a series of recognizable families. The individual members of these families have certain structural characteristics that define their membership. These common features are described and their functions are analyzed in supramolecular terms. Once identified, these key characteristics can then be retained during the synthesis of new family members. A number of clathrand hosts are known that contain structural features associated with two or more of the basic clathrate families. These compounds are described and their relationship with multiple host families is delineated. Finally, the chapter examines the current state of play in this research area. Recent advances and current difficulties are highlighted.

Multimolecular Weak-Force Tectons and Their Alternative Clathrate Forms

“…It is employed to shore up the walls of the host cavity against collapse in an almost perfect analogy with excavation engineering practices. To the best of our knowledge, such behavior has not been previously recorded in the inclusion chemistry area, despite the frequent presence of tubes and cages in such materials. , …”

“…For example, whereas the tetrahedrally shaped molecule 1 packs compactly and efficiently in its crystals, its cousin 2 definitely does not. Typical Pauling hydrogen bonding occurs at each of the four tetrahedral vertices of 2 to generate a highly porous three-dimensional network. , Around 60% of this tetrapyridinone crystal volume is available for guest occupancy in the form of inclusion compounds. , …”

Organic crystal engineering beyond the Pauling hydrogen bond

“…24 Aromatic interactions are widely used to make host molecules include another type (the guest) within their crystals. [25][26][27] Hydrocarbons such as 8 and 9 have a twisted propeller shape, pack inefficiently by themselves, 28 and therefore include guests to raise their packing coefficients. Kekulé, of aromaticity fame, was the first to report this behaviour in 1872 for the benzene compound of triphenylmethane 8.…”

Swivel and Tilt Interactions: Directional Change in Aromatic π···π Crystal Packing

“…Structural properties are frequently investigated by utilizing compilations of crystallographic information. − Our studies on diquinoline inclusion hosts , have generated over a hundred crystal structure determinations. Analysis of these data has enabled systematic crystal engineering studies of interactions weaker than the Pauling hydrogen bond to be carried out successfully. − Figure illustrates the generic design of these compounds.…”