Continuous Breathing Rare-Earth MOFs Based on Hexanuclear Clusters with Gas Trapping Properties

Abstract

Guest responsive porous materials represent an important and fascinating class of multifunctional solids that have attracted considerable attention in recent years. An understanding of how these structures form is essential toward their rational design, which is a prerequisite for the development of tailor-made materials for advanced applications. We herein report a novel series of stable rare-earth (RE) MOFs that show a rare continuous breathing behavior and an unprecedented gas-trapping property. We used an asymmetric 4-c tetratopic carboxylate-based organic ligand that is capable of affording highly crystalline materials upon controlled reaction with RE cations. These MOFs, denoted as RE-thc-MOF-1 (RE: Y3+, Sm3+, Eu3+, Tb3+, Dy3+, Ho3+, and Er3+), feature hexanuclear RE6 clusters that display a highly unusual connectivity and serve as unique 8-c hemi-cuboctahedral secondary building block, resulting in a new (3,3,8)-c thc topology. Extensive single-crystal to single-crystal structural analyses coupled with detailed gas (N2, Ar, Kr, CO2, CH4, and Xe) and vapor (EtOH, CH3CN, C6H6, and C6H14) sorption studies, supported by accurate theoretical calculations, shed light onto the unique swelling behavior. The results reveal a synergistic action involving steric effects, associated with coordinated solvent molecules and 2-fluorobenzoate (2-FBA) nonbridging ligands, as well as cation–framework electrostatic interactions. We were able to probe the individual role of the coordinated solvent molecules and 2-FBA ligands and found that both cooperatively control the gas-breathing and -trapping properties, while 2-FBA controls the vapor adsorption selectivity. These findings provide unique opportunities toward the design and development of tunable RE-based flexible MOFs with tailor-made properties.

Fluoro-Bridged Clusters in Rare-Earth Metal–Organic Frameworks

“…The use of fluorinated modulators, such as 2-fba or 2,6-dfba (Figure ), has been widely and successfully implemented in the area of RE MOFs, always with reports of μ 3 -OH-bridged clusters in their structures (Table S1). − …”

“…If the presence of fluorine is indeed confirmed in these RE MOFs, some of the observed properties could be attributed to the fluoro-bridged RE clusters (Table S1). ,− For example, in a recent report, a terbium hexacluster containing μ 3 -F bridges was compared to the μ 3 -OH-bridged analogue . The fluorinated compound had higher photoluminescence, a property reported in some of these MOFs.…”

2-Dimensional rare earth metal–organic frameworks based on a hexanuclear secondary building unit as efficient detectors for vapours of nitroaromatics and volatile organic compounds

“…Although several examples of RE 3+ MOFs based on the hexanuclear SBU have been reported, the vast majority is 3D compounds. 45,48,49,53,[73][74][75][76] To the best of our knowledge, com-pound UCY-15(RE) is only the second example of a 2D MOF based on (RE 3+ ) 6 -SBU. 77 The existence of a very limited number of 2D MOFs based on a (RE 3+ ) 6 -SBU is rationalized on the basis of the presence of several carboxylate groups connecting the RE 3+ ions of the SBU due to the extended and flexible coordination sphere of these ions leading to 3D structures.…”

A Li-based MOF-derived multifunctional PEO polymer solid-state electrolyte for lithium energy storage

“…Metal–organic framework (MOF) materials possess fascinating architectures and a wide range of potential applications, particularly in gas storage, chemical separation, drug delivery, catalysis, energy storage and chemo-sensing. 36–41 Recently, MOFs have been widely investigated in energy storage systems as both active materials and separators due to their unique properties. MOF additives in SSPEs have exhibited improved ionic conductivities and superior interfacial properties due to their low modulus.…”