Modulated Self-Assembly of an Interpenetrated MIL-53 Sc Metal-Organic Framework with Excellent Volumetric H2 Storage and Working Capacity

Abstract

To achieve optimal performance in gas storage and delivery applications, metal-organic frameworks (MOFs) must combine high gravimetric and volumetric capacities. One potential route to balancing high pore volume with suitable crystal density is interpenetration, where identical nets sit within the void space of one another. Herein, we report an interpenetrated MIL-53 topology MOF, named GUF-1, where one-dimensional Sc(µ2-OH) chains are connected by 4,4’-(ethyne-1,2-diyl)dibenzoate linkers into a material that is an unusual example of an interpenetrated MOF with a rod-like secondary building unit. A combination of modulated self-assembly and grand canonical Monte Carlo simulations are used to optimise the porosity of GUF-1; H2 adsorption isotherms reveal a very high Qst for H2 of 7.6 kJ mol-1 and a working capacity of 41 g L-1 in a temperature-pressure swing system, which is comparable to benchmark MOFs. These results show that interpenetration is a viable route to high performance gas storage materials comprised of relatively simple building blocks.

Pressure-Induced Postsynthetic Cluster Anion Substitution in a MIL-53 Topology Scandium Metal-Organic Framework

“…We recently reported the synthesis, structure, and excellent H2 storage capacity of GUF-1. 47 As its interpenetration results in limited breathing in comparison to non-interpenetrated MIL-53 topology MOFs, 49,50 allied to the fact that it has a potentially flexible EDB 2linker, we sought to characterise its structural response to pressure using high-pressure single crystal X-ray diffraction in a DAC. This approach 51 has previously allowed us and others to characterise mechanical compliance of a range of MOFs, [52][53][54][55][56][57] as well as to investigate the structural basis of spectroscopic responses to pressure and different guests.…”

“…This approach 51 has previously allowed us and others to characterise mechanical compliance of a range of MOFs, [52][53][54][55][56][57] as well as to investigate the structural basis of spectroscopic responses to pressure and different guests. 58,59 Single crystals of GUF-1-(HCl) were prepared according to our previously reported HCl modulated solvothermal synthesis in N,N-dimethylformamide (DMF), 47 and transferred into fresh DMF for storage (see supplementary information, Section S2). Under ambient conditions, GUF-1 forms pale pink cuboidal crystals in the orthorhombic space group, Cmme.…”

“…One is decorated by μ2-OH groups at the shared corners of ScO6 pairs, and contains two DMF molecules from the crystallisation solvent per unit formula, with a hydrogen bonding interaction between the formyl group of the DMF and the H atom of the bridging hydroxide (O⸱⸱⸱O = 2.89(2) Å). 47 The second channel is vacant upon synthesis, with a solvent accessible volume of 270 Å 3 (probe radius = 1.2 Å, grid spacing = 0.7 Å, Mercury, CSD). 60 A single crystal of GUF-1-(HCl) was transferred from DMF storage and compressed in a modified Merrill-Bassett DAC 61 using methanol (CH3OH) as the pressure-transmitting medium; CH3OH is a commonly used solvent which is small enough to infiltrate the framework pores and remains liquid to high pressures (see supplementary information, Section S3).…”

“…Herein, we report the pressure-induced reactivity of the SBU of the Sc MOF GUF-1 (GUF = Glasgow University Framework), where the 4,4ʹ-(ethyne-1,2-diyl)dibenzoate (EDB 2-) ligand links one-dimensional ScOH SBUs into a two-fold interpenetrated net with the MIL-53 topology and overall formula [ScOH(EDB)]n. 47 Using high-pressure techniques alongside solid-state NMR spectroscopy, we show that up to 17(2)% of bridging µ2-OH ligands can be replaced by bridging µ2-OCH3 units in the bulk phase by reaction with methanol at 0.8 GPa in a large volume press, with conversions of up to 98(4)% in a single crystal pressurised to 4.98 GPa in methanol in a diamond anvil cell (DAC) observed by single crystal X-ray diffraction. This is at least an order of magnitude higher than analogous reactivity under ambient conditions, and represents a rare example of pressure-induced postsynthetic modification of MOFs 48 with significant implications for their activation with methanol, and processing and shaping for application.…”