Stabilization of Scandium Terephthalate MOFs against Reversible Amorphization and Structural Phase Transition by Guest Uptake at Extreme Pressure

Abstract

Previous high-pressure experiments have shown that pressure-transmitting fluids composed of small molecules can be forced inside the pores of metal organic framework materials, where they can cause phase transitions and amorphization and can even induce porosity in conventionally nonporous materials. Here we report a combined high-pressure diffraction and computational study of the structural response to methanol uptake at high pressure on a scandium terephthalate MOF (Sc2BDC3, BDC = 1,4-benzenedicarboxylate) and its nitro-functionalized derivative (Sc2(NO2-BDC)3) and compare it to direct compression behavior in a nonpenetrative hydrostatic fluid, Fluorinert-77. In Fluorinert-77, Sc2BDC3 displays amorphization above 0.1 GPa, reversible upon pressure release, whereas Sc2(NO2-BDC)3 undergoes a phase transition (C2/c to Fdd2) to a denser but topologically identical polymorph. In the presence of methanol, the reversible amorphization of Sc2BDC3 and the displacive phase transition of the nitro-form are completely inhibited (at least up to 3 GPa). Upon uptake of methanol on Sc2BDC3, the methanol molecules are found by diffraction to occupy two sites, with preferential relative filling of one site compared to the other: grand canonical Monte Carlo simulations support these experimental observations, and molecular dynamics simulations reveal the likely orientations of the methanol molecules, which are controlled at least in part by H-bonding interactions between guests. As well as revealing the atomistic origin of the stabilization of these MOFs against nonpenetrative hydrostatic fluids at high pressure, this study demonstrates a novel high-pressure approach to study adsorption within a porous framework as a function of increasing guest content, and so to determine the most energetically favorable adsorption sites.

Neon‐Bearing Ammonium Metal Formates: Formation and Behaviour under Pressure

“…In summary, our results have shown that neon, one of the most inert atoms, is able to form an inclusion compound with ammonium metal formates at high pressures. While other examples of either noble gas (He or Ar) or small‐molecule inclusions are known within porous network solids at high pressure, here we observe that the closed porosity of AMF at ambient conditions becomes accessible for inclusion of neon under pressure. This highlights the facile movement of the ammonium cations for allowing neon insertion throughout the metal formate structure upon compression and neon release upon decompression.…”

“…The formation of neon‐bearing network solids can give several insights into the properties of the empty and filled network states. For example, pore dimensions can be rigorously evaluated as a function of temperature from the decapsulation peak profiles of He and Ne, the thermodynamic stability may be increased as found in neon clathrate hydrates, and the mechanical properties of the filled and empty network states can be drastically different, as known with other inclusion species . A combination of structural and computational investigations on the neon‐bearing network solids can provide fundamental information on neon‐neon and neon‐network interactions, which may be used towards synthesis strategies that aim to stabilise exotic chemically‐bound neon compounds as known with the heavier noble gases …”

“…[11][12][13][14] The formation of neon-bearing network solids can give several insights into the properties of the empty and filled network states.F or example, pore dimensionsc an be rigorously evaluated as af unction of temperature from the decapsulation peak profiles of He and Ne, [14] the thermodynamic stabilitym ay be increased asf ound in neon clathrate hydrates, [9] and the mechanical properties of the filled and empty network states can be drastically different, ask nown with other inclusion species. [15][16][17][18][19][20][21][22][23][24][25] Ac ombination of structural and computational investigationso nt he neon-bearing network solids can provide fundamental information on neon-neon and neon-network interactions, [9] which may be used towardss ynthesis strategies that aim to stabilisee xotic chemically-bound neon compoundsa s knownw iththe heavier noble gases. [26,27] Selective noble gas encapsulation or adsorption is of interest for the development of noble gas purification processes, as it provides ac heaper alternative to the cryogenic distillation techniques used currently.A lready,asubstantial research progress hasb een achieved towards the selective adsorption of Xe over Kr using specific pore sizes and shapes within extended network solids, [28] particularly using metal-organic frameworks (MOFs).…”

Locating Gases in Porous Materials: Cryogenic Loading of Fuel‐Related Gases Into a Sc‐based Metal–Organic Framework under Extreme Pressures

“…A small increase in the unit cell volume of <1% was observed at 3 kbar, which is a frequent observation in other high-pressure inclusion studies on other MOFs including Sc2BDC3. [11,15] As seen with the inclusion of methanol, the expansion seemed to rely mostly on an increase along the a-axis, which corresponds to the channel directions (SI-IV). The continued increase of the a-axis with increasing pressure is in line with further CH4 being forced inside the framework, but overall the unit cell volume started to decrease above 6 kbar.…”

Group 3 Elements and Lanthanide Metals

“…Among scandium variants of terephthalate and trimesate MOFs, MIL-100(Sc) was reported as highly Lewis acidic catalyst suitable for C-C bond formation [37]. Other than that, the terephthalate MOFs Sc 2 BDC 3 (BDC = 1,4-benzenedicarboxylate) and its nitro-functionalized derivative (Sc 2 (NO 2 -BDC) 3 ) were reported very recently and investigated regarding high pressure uptake of methanol [38].…”