Networked molecular cages as crystalline sponges for fullerenes and other guests

Abstract

Many molecular cages selectively bind guests in solution, but in the solid state close packing often prevents guest entry, which renders the cages inactive. We envisioned that coordination networks constructed from well-known molecular cages could transfer the richness of solution-state host-guest chemistry into the solid state. We report a crystalline coordination network generated from an infinite array of octahedral M(6)L(4) cage subunits (M = metal, L = ligand). This coordination network is a 'crystalline molecular sponge' engineered on the molecular level and retains similar guest recognition properties to those found in solution. The network crystallinity is robust and thus X-ray diffraction analysis can be used to unambiguously observe single-crystal to single-crystal guest inclusion. The void spaces define alternating M(12)L(8) and M(12)L(24) cuboctahedral molecular cages and these large cages absorb up to 35 weight per cent of C(60) or C(70) by simply soaking the crystals in a toluene solution of the fullerene. When the crystals are immersed in fullerene mixtures, C(70) is preferentially absorbed.

Sponge-like molecular cage for purification of fullerenes

“…14) 53 in a C 70 -containing toluene solution, thus being the first example of solid-phase fullerene encapsulation for a supramolecular cage (to our knowledge, a single similar precedent using a MOF was reported by Fujita and co-workers) 46 . This observation discards partial cage disassembly during the host-guest event, and agrees with a guest encapsulation occurring by fullerene entrance through the four apertures of the cage; the dimensions of the apertures are large enough to envision the mobility of fullerene molecules through them.…”

“…Interestingly, Fujita and co-workers reported the use of the empty channels of a metal-organic framework (MOF) for encapsulating fullerenes upon soaking MOF crystals in fullerene-containing toluene. This work is remarkable because it explores the ability of a solid crystalline structure to absorb fullerenes into its large pores by displacing solvent molecules 46 .…”

“…In all reported examples, however, there is the need to expose the host to chemical or physical treatment to release the sequestered guests, which prevent its straightforward reusability either because it is blocked by a high-affinity secondary guest, or because the host cage is disassembled. In the case of Fujita's crystalline sponge strategy 46 , the retention capability is high and half lives of inclusion complexes are over 15 days, thus release of fullerenes must be achieved by deconstructing MOF crystals by acid treatment.…”

Influence of Bio-Isosteric Replacement on the Formation of Templating Methanol and Acetonitrile Solvates in Lophines

“…26,27 Inclusion complexes have recently become focus of attention to study the incorporated molecules, either in an unusual conformation, 28 or to obtain structural information of a hard to crystallise compound. 29,30 Considering the variation in size and interaction potential in bio-isosteric groups, the choice of replacement group will influence the crystal structure of the substances, as has recently been shown for a series of trityl compounds. 31 In addition, change of halogen substituents from chloro via bromo to iodo on phloroglucinol has been shown to influence the incorporation mode of water into the crystal structure.…”

Adamantane-based Bidendate Metal Complexes in Crystalline and Solution State

“…[1][2][3][4][5] Metal-mediated architectures have unique applications as functional crystalline materials in catalysis, 6,7 guest inclusion, [8][9][10][11][12][13][14][15] photochemistry [16][17][18][19] and gas storage. [20][21][22][23][24][25][26] The diversity of metal-directed molecular networks is markedly dependent on the ligand and the coordination geometry of the metal ions.…”