Noninvasive Substitution of K⁺ Sites in Cyclodextrin Metal–Organic Frameworks by Li⁺ Ions

Abstract

Co-crystallization of K and Li ions with γ-cyclodextrin (γ-CD) has been shown to substitute the K ion sites partially by Li ions, while retaining the structural integrity and accessible porosity of CD-MOF-1 (MOF, metal-organic framework). A series of experiments, in which the K/Li ratio was varied with respect to that of γ-CD, have been conducted in order to achieve the highest possible proportion of Li ions in the framework. Attempts to obtain a CD-MOF containing only Li ions resulted in nonporous materials. The structural occupancy on the part of the Li ions in the new CD-MOF has been confirmed by single-crystal X-ray analysis by determining the vacancies of K-ion sites and accounting for the cation/γ-CD ratio in CD-MOF-1. The proportion of Li ions has also been confirmed by elemental analysis, whereas powder X-ray diffraction has established the stability of the extended framework. This noninvasive synthetic approach to generating mixed-metal CD-MOFs is a promising method for obtaining porous framework unattainable de novo. Furthermore, the CO and H capture capacities of the Li-ion-substituted CD-MOF have been shown to exceed the highest sorption capacities reported so far for CD-MOFs.

Intrinsically porous molecular building blocks for metal organic frameworks tailored by the bridging effect of counter cations

“…Naturally occurring γ-cyclodextrin (γ-CD) have been successfully used in building CD-MOFs with permanent porosity and the ability to store small molecules in their pores. [13][14][15] Recently, we have communicated the use of CDs combined with inorganic polyoxometalates (POMs) [16][17][18] as MBBs to prepare a new generation of porous hybrid frameworks (POM-CD MOFs). 19 These assemblies benefited from the intrinsic microporosity and functional multiplicity of both isolated building blocks.…”

Crystal structure of a two-dimensional metal–organic framework assembled from lithium(I) and γ-cyclodextrin

“…Metal-organic frameworks (MOFs) based on cyclodextrin were developed by the Stoddart group and have been known for almost ten years (Smaldone et al, 2010). Many cyclodextrin MOFs with various alkali metal ions have been obtained so far (Patel et al, 2017;Bagabas et al, 2013). Exceptions are lithium ion-based MOFs because all of the compounds obtained that have been reported in the literature contain two different metal ions in the crystal structure (Bagabas et al, 2013;Patel et al, 2017).…”

“…Many cyclodextrin MOFs with various alkali metal ions have been obtained so far (Patel et al, 2017;Bagabas et al, 2013). Exceptions are lithium ion-based MOFs because all of the compounds obtained that have been reported in the literature contain two different metal ions in the crystal structure (Bagabas et al, 2013;Patel et al, 2017). Lithiumbased MOFs are among the best candidates for electrode materials for lithium-ion batteries because of their high porosity and structural control (Baumann et al, 2019;Sharma et al, 2019).…”

Inedible saccharides: a platform for CO2 capturing

“…The high volatility associated with CO 2 BOLs and the hardship of drying/handling, together with the high corrosive character, paved the way toward single component CO 2 BOLs 17 ( Scheme 1C ) that unfortunately exhibited high viscosity upon chemisorption. Afterwards, Sir J. F. Stoddart’s group 41 – 44 reported that the hydroxyl groups located at the rim of γ-cyclodextrin-based metal–organic frameworks (CD-MOFs) are capable of reacting with CO 2 reversibly to form a metal-stabilized organic alkyl-carbonate (a detailed discussion is provided, vide infra ).…”

“…The challenge in synthesizing CD-MOFs with cations other than K + , Rb + and Cs + , is the inability to obtain porous, crystalline frameworks. Very recently, Patel et al 44 demonstrated the partial substitution of K + with Li + through co-crystallizing KOH and LiOH with γ-CD. As shown in Table 1 , the most stable Li/K–CD-MOF with the highest Li + : K + ratio (0.61 : 1.18) had a comparable Brunauer–Emmett–Teller (BET) surface area and a characteristic better sorption in comparison with those obtained for other iso-structural CD-MOFs.…”