Many Simple Molecular Cavitands Are Intrinsically Porous (Zero-Dimensional Pore) Materials

Abstract

The guest-free crystal forms of eight related small molecule cavitands (Scheme 1; simplified nomenclature: R,R',Y) are investigated as candidate discrete molecule microcavity materials (DMMMs). Due to their rigid bowl-like molecular structures, many cavitands are incapable of efficient crystal packing in pure form, yielding zero-dimensionally porous apohost phases. By molecular modifications that eschew self-inclusion, emphasis is placed on engineering structures that exhibit uniform microcavities that are large enough to accommodate small molecules of interest (e.g., gases or volatile organic compounds). The most thermodynamically stable guest-free crystal forms of several cavitands-namely, H,H,CH 2 , H,Me,CH 2 , α-Me,H,CH 2 , Me,Me,CH 2 , Br,Me,CH 2 , Me,Et,CH 2 , Me,Et,SiMe 2 , and Me,i-Bu,CH 2 -appear to be as-close-packed-as-possible, yet exhibit relatively large microcavities (or, zero-dimensional pores) in the range of 27-115 Å 3 . Where self-inclusion is ineffective, the microcavities predictably assimilate the intrinsic cavitand molecular cavity, yet the ultimate size and shape of cavities are also strongly influenced by crystal packing. It is demonstrated that some cavitand solvates, CH 2 Cl 2 @H,Me,CH 2 , xH 2 O@Me,Et,SiMe 2 , and CH 2 Cl 2 @Me,iBu,CH 2 (84:16 rccc:rcct) maintain host crystal packings that are equivalent to their empty, intrinsically porous phases and it is argued that the intrinsic pores of DMMMs are particularly suited to selective gas enclathration and/or storage. As a proof-ofconcept demonstrations, the porous phase of Me,Et,SiMe 2 is shown to capture and temporarily hold Freon-41 (fluoromethane, bp = -78 °C) at room temperature. A single crystal of empty Me,Et,SiMe 2 is shown to uptake CO 2 gas at room temperature, allowing structure determination of xCO 2 @Me,Et,SiMe 2 , and single-crystal-to-single-crystal dehydration of xH 2 O@Me,Et,SiMe 2 demonstrates its permeability to water.

A chiral member of the family of organic hexameric cages

“…Considering the rigid skeleton of 3, the capsule can be considered as a shape-persistent cage possessing an intrinsic porosity also in the solid state due to presence of internal and external cavities. [38][39][40][41][42][43][44] Analysis of packing in the crystal network indicates that although the capsules are relatively dense-packed with small intercapsular voids, they pack in a window-towindow arrangement (Fig. 5b).…”

From Concept to Crystals via Prediction: Multi-Component Organic Cage Pots by Social Self-Sorting

“…[23] These chiral organic cage pots have analogies to hemicryptophanes, [40] which suggests that they might be of interest for the formation of guest-host complexes with the potential to encapsulate guests (e.g., rare gases,such as xenon). [41,42] Figure 4. a) Synthesis of the self-sortedc age pot OCP3,formed from the reaction of atri-topic aldehyde with both di-topic and tri-topic amines.…”

Exploring the Scope of Macrocyclic “Shoe-last” Templates in the Mechanochemical Synthesis of RHO Topology Zeolitic Imidazolate Frameworks (ZIFs)

“…The MeMeCH 2 [32] cavitand was used to template reactions employing 4,5-dichloroimidazole (HCl 2 Im), benzimidazole (HBIm), 5-nitrobenzimidazole (HNO 2 BIm), 5,6-dimethylbenzimidazole (HMe 2 BIm), and theophylline (Theo). Nine cavitands were explored as possible templates in reaction with the simple imidazole (HIm) ligand: HPhCH 2 [57], H(4-MePh)CH 2 [57], MeHCH 2 [55], MeHCH 2 -6 [55], MeHSiMe 2 [58], MeiBuCH 2 [56], MePhCH 2 [59], BrC5CH 2 [60] and BrPhCH 2 [57]. All cavitands were prepared according to literature procedures [32] and were used in unsolvated form, after drying in a vacuum oven (Precision Scientific, Chicago, IL, USA) at 120 • C for 24 h. The resulting dense paste was transferred to a 5 mL glass vial and left to age.…”

“…Comparison of the crystal structures of MeHCH2 (left; CSD code VUWMIL[56]) and MeHCH2-6 (right; CSD code QUCWOA[55], chloroform solvate, solvent molecules omitted for clarity), illustrating the similarities of a portion of their molecular structures. (a) top view, (b) side view.…”