Tunable Fulleretic Sodalite MOFs: Highly Efficient and Controllable Entrapment of C₆₀ Fullerene via Mechanochemistry

Abstract

Encapsulation and confinement of fullerene guests in metal-organic frameworks (MOFs) lead to a novel class of crystalline fulleretic materials with unique physicochemical properties and a broad field of potential applications. The control over the amount of target guests confined in the MOF structure remains a significant challenge, which is particularly pronounced in the confinement of hardly accessible fullerene derivatives. The main strategies used in constructing fulleretic composites are limited by the solubility of components used and solvent versus guest competition for inhabitation of the framework voids. As mechanochemical procedures often overcome these issues, we developed here solvent-free processing by ball milling to gain control over the encapsulation of bulky and rigid C 60 -fullerene into a sodalite MOF with large cages and narrow cage-apertures. A rapid, green, efficient, and stoichiometry-controlled mechanochemical processing afforded four model C 60 @zeolitic-imidazolate framework 8 (ZIF-8) crystalline materials containing target 15, 30, 60, and 100 mol % of fullerene entrapped in the accessible cages of the model sodalite zeolitic-imidazolate framework 8 (ZIF-8), in stark contrast to the solution-based strategies that resulted in almost no loading. Varying the fullerene content affects the framework's vibrational properties, color and luminescence of the composites, and the electron-dose radiation stability. The computational and spectroscopic studies show that the fullerene is accommodated in the cage's center and that the cage-to-cage transport is a hardly feasible and energetically unfavored process. However, the fast release of C 60 molecules from ZIF-8 can be effectively controlled by the pH. The entrapment of fullerene molecules in ZIF-8 resulted in their effective isolation even in higher loadings, paving the way to other tunable porous fulleretics containing single-molecule magnets or nanoprobes available on low scales.

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes

“…[22][23][24] However, obtaining a large exchange coupling between two Ln 3+ metal ions is a formidable task as 4f orbitals are deeply buried, leading to a weak/no interaction in dinuclear or polynuclear Ln 3+ complexes. 8,[25][26][27][28][29][30] In this regard, lanthanide encapsulated fullerenes (called endohedral metallofullerenes or EMFs) are gaining tremendous attention for various reasons (a) they offer stability to the guest molecules which are otherwise unstable 31 (b) thanks to their strong  cloud, fabrication of such molecules on Graphene/HOPG/CNTs and other surfaces are straightforward [31][32][33][34][35][36][37][38][39] (c) during this process the guest molecules stay intact, and hence they are unlikely to lose their characteristics upon fabrication 31 (d) as fullerenes are made of pure carbon, and the source of nuclear spin of the guest molecules can be controlled, they offer a nuclear spin free systems -a key criterion for some Q-bits applications. 31,40 These key advantages mentioned here directly address the aforementioned goals (ii) and (iii), making them superior to traditional coordination chemistry/organometallic SMMs/SIMs.…”

Mechano‐Nanoarchitectonics: Design and Function

“…For example, Popov and co-workers demonstrated solvent-free mechanical processes for controlled supramolecular inclusion of fullerene (C 60 ) molecules into metal-organic framework (MOF). [36] Inclusion of C 60 molecules with bulky and rigid features into sodalite MOF materials of zeoliticimidazolate framework 8 (ZIF-8) crystals with narrow cageapertures was achieved by a simple mechanical process of ball milling. While solution processes of these components do not lead to any encapsulation, the above-mentioned mechanical ball milling resulted in facilitated inclusion with controlled encapsulation ratios up to 100 mol% of fullerene per accessible cages of the ZIF-8 materials.…”

Infrared spectroscopic monitoring of solid-state processes

“…IR spectroscopy is often employed to monitor the occupation of the pores in porous materials, such as metal-organic frameworks (MOF), [167][168][169][170] zeolites, [171][172][173][174] porous carbons 166,[175][176][177] etc. 178 IR spectroscopy can confirm the successful and controllable preparation of C 60 encapsulated inside the pores of zeoliticimidazolate framework 8 (ZIF-8) by solvent-free mechanochemical processes.…”