Crystallography of encapsulated molecules

Abstract

The crystallography of supramolecular host-guest complexes is reviewed and discussed as a part of small molecule crystallography. In these complexes, the host binds the guests through weak supramolecular interactions, such as hydrogen and halogen bonding, cation-π, anion-π, C-H-π, π-π, C-H-anion interactions and the hydrophobic effect. As the guest often shows severe disorder, large thermal motion and low occupancies, the reliable crystallographic determination of the guest can be very demanding. The analysis of host-guest interactions using tools such as Hirshfeld and cavity volume surface analysis will help to look closely at the most important host-guest interactions. The jewel in the crown of utilizing host-guest interactions in the solid-state is the recently developed Crystalline Sponge Method (CSM) by Makoto Fujita. This method, when successful, gives an accurate and unambiguous 3-D structure of the structurally unknown guest molecule from only micro- or nanogram amounts of the guest molecule. In the case of an optically pure enantiomer, its absolute configuration can be determined.

One Guest or Two? A Crystallographic and Solution Study of Guest Binding in a Cubic Coordination Cage

“…We prepared the cage/guest complexes for crystallographic studies in this paper using the “crystalline sponge“ method, famously recently popularised in supramolecular chemistry by the work of Fujita's group . This involved treating pre‐formed crystals of host H with guests which could be taken up into the crystals without loss of crystallinity.…”

Supramolecular Organization in Confined Nanospaces

“…[30] for a review) but also to analytic methodologies. The so‐called “crystalline sponge” approach refers to the preparation of composites in which guest molecules are trapped into MOF cages and then studied by crystallographic methods . In practice, carefully selected frameworks absorb target molecules from a solution, thus converting the incoming liquid into an arrangement of confined guest species thanks to the molecular‐recognition ability of MOF cavities .…”

“…In practice, carefully selected frameworks absorb target molecules from a solution, thus converting the incoming liquid into an arrangement of confined guest species thanks to the molecular‐recognition ability of MOF cavities . In this manner, the geometrical features of the absorbed species could be revealed, along with the host framework, by X‐ray analysis of the porous composite material, thus making structure elucidation possible even for compounds very difficult to crystallize ,. Besides the obvious advantages, the method suffers from limitations: i) structure resolution is not always successful, ii) pore confinement in some cases alters significantly the physicochemical properties of both the guest species and the host, as evidenced by a recent study …”

Steric and Electronic Effect on C2‐H Arylation of Sulfonamides

“…The nature of the chemical reactions can be controlled by the influence of weak interactions or soft force . Therefore, many reactions are designed by exploring cooperative multiple non‐covalent interactions like hydrogen bonding, halogen bonding, hydrophobic effect, cation‐π, anion‐π, etc . Our research goal is encircled in understanding the reactivity of non‐prefunctionalized substrates by weak or noncovalent interactions .…”